31 results on '"Mongkolsuk, S."'
Search Results
2. Isolation and analysis of the Xanthomonas alkyl hydroperoxide reductase gene and the peroxide sensor regulator genes ahpC and ahpF-oxyR-orfX
- Author
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Loprasert, S, primary, Atichartpongkun, S, additional, Whangsuk, W, additional, and Mongkolsuk, S, additional
- Published
- 1997
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3. Heterologous growth phase- and temperature-dependent expression and H2O2 toxicity protection of a superoxide-inducible monofunctional catalase gene from Xanthomonas oryzae pv. oryzae
- Author
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Mongkolsuk, S, primary, Loprasert, S, additional, Vattanaviboon, P, additional, Chanvanichayachai, C, additional, Chamnongpol, S, additional, and Supsamran, N, additional
- Published
- 1996
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4. Chloramphenicol-induced translation of cat-86 mRNA requires two cis-acting regulatory regions
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Ambulos, N P, Mongkolsuk, S, Kaufman, J D, and Lovett, P S
- Abstract
Sequences essential to the chloramphenicol-inducible expression of cat-86, a chloramphenicol acetyltransferase gene, reside in a 144-base pair (bp) regulatory region that intervenes between the cat-86 coding sequence and its promoter. A key regulatory element within the 144-bp segment consists of a pair of inverted-repeat sequences that immediately precede the cat-86 coding region and span the ribosome-binding site for the gene. Because of the location of the inverted repeats, cat-86 transcripts are predicted to sequester the ribosome-binding site in a stable RNA stem-loop structure which should block translation of cat-86 mRNA. Chloramphenicol induction of gene expression is believed to result from ribosome-mediated destabilization of the RNA stem-loop structure, which frees the cat-86 ribosome-binding site, thereby allowing translation. In this study we demonstrated that deletion of 85 bp from the 5' end of the 144-bp regulatory region abolishes inducible expression of cat-86, although the gene is transcribed. This deletion leaves intact both the inverted repeats and the cat-86 coding sequence, and the deletion mutation is not complementable. Therefore, inducible regulation of cat-86 requires the inverted repeats plus an upstream, cis-acting regulatory region. The cis-acting region is believed to control translation of cat-86 mRNA by its essential participation in chloramphenicol-induced opening of the RNA stem-loop. cat-86 deleted for the 85-bp regulatory region and therefore virtually unexpressed was used to select for mutations that restore expression to the gene. An analysis of one mutant plasmid showed that the cat-86 gene is constitutively expressed and that this results from a duplication of the DNA sequence that spans the ribosome-binding site. The duplication provides cat-86 with two ribosome-binding sites. One of these sites is predicted to be sequestered in an RNA stem-loop, and the other is not involved in RNA secondary structure.
- Published
- 1985
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5. Chloramphenicol-inducible gene expression in Bacillus subtilis is independent of the chloramphenicol acetyltransferase structural gene and its promoter
- Author
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Mongkolsuk, S, Ambulos, N P, and Lovett, P S
- Abstract
cat-86 specifies chloramphenicol acetyltransferase and is the indicator gene on the Bacillus subtilis promoter cloning plasmid pPL703. Insertion of promoters from various sources into pPL703 at a site ca. 144 base pairs upstream from cat-86 activates expression of cat-86, and the expression is characteristically inducible by chloramphenicol. Thus, chloramphenicol inducibility of cat-86 is independent of the promoter that is used to activate the gene. To determine whether cat-86 or its products were involved in chloramphenicol inducibility, gene replacement studies were performed. cat-86 consists of 220 codons. The lacZ gene from Escherichia coli was inserted into a promoter-containing derivative of pPL703, plasmid pPL603E, at two locations within cat-86. pPL3lac2 contains lacZ inserted in frame after codon 2 of cat-86. pPL3lac30 contains lacZ inserted in frame after codon 30 of cat-86. In both constructions, all cat coding sequences 3' to the site of the lacZ insertion were deleted. Both plasmids exhibited chloramphenicol inducibility of beta-galactosidase in B. subtilis. These studies provide the first direct demonstration that the transcription and translation products of a chloramphenicol-inducible cat gene are uninvolved in chloramphenicol inducibility of gene expression. The results localize the region essential to inducibility to the 144-base pair segment that intervenes between the site of promoter insertion and the cat-86 gene.
- Published
- 1984
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6. Induction of the chloramphenicol acetyltransferase gene cat-86 through the action of the ribosomal antibiotic amicetin: involvement of a Bacillus subtilis ribosomal component in cat induction
- Author
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Duvall, E J, Mongkolsuk, S, Kim, U J, Lovett, P S, Henkin, T M, and Chambliss, G H
- Abstract
The plasmid gene cat-86 and the cat gene resident on pC194 each encode chloramphenicol-inducible chloramphenicol acetyltransferase activity in Bacillus subtilis. Chloramphenicol induction has been proposed to result from chloramphenicol binding to ribosomes, which then permits the drug-modified ribosomes to perform events essential to induction. If this proposal were correct, B. subtilis mutants containing chloramphenicol-insensitive ribosomes should not permit chloramphenicol induction of either cat-86 or pC194 cat. However, we and others have been unable to isolate chloramphenicol-resistant ribosomal mutants of B. subtilis 168. We therefore developed a simple procedure for screening other antibiotics for the potential to induce cat-86 expression. One antibiotic, amicetin, was found to be an effective inducer of cat-86 but not of the cat gene on pC194. Amicetin and chloramphenicol each interact with the 50S ribosomal subunit, and the mechanism of cat-86 induction by both drugs may be similar. Amicetin-resistant mutants of B. subtilis were readily isolated, and in none of six mutants tested was cat-86 detectably inducible by amicetin, although the chloramphenicol-inducible phenotype was retained. The ami-1 mutation which is present in one of these amicetin-resistant mutants was mapped by PBS1 transduction to the "ribosomal gene cluster" adjacent to cysA. Additionally, ribosomes from cells harboring the ami-1 mutation contained an altered BL12a protein, as detected in two-dimensional polyacrylamide gel electrophoresis. Lastly, an in vitro protein-synthesizing system that uses ribosomes from an ami-1-containing cell line was more resistant to amicetin than a system that uses ribosomes from an amicetin-sensitive but otherwise isogenic strain. These results indicate that the host mutation, ami-1, which effectively abolished the inducibility of cat-86 by amicetin, altered a ribosomal component.
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- 1985
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7. Regulatory regions that control expression of two chloramphenicol-inducible cat genes cloned in Bacillus subtilis
- Author
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Duvall, E J, Williams, D M, Mongkolsuk, S, and Lovett, P S
- Abstract
Plasmid pPL603 is a promoter cloning vector for Bacillus subtilis and consists of a 1.1-kilobase fragment of Bacillus pumilus DNA inserted between the EcoRI and BamHI sites of pUB110. The gene cat-86, specifying chloramphenicol-inducible chloramphenicol acetyltransferase, is located on the 1.1-kilobase cloned DNA. When pPL603 is present in B. subtilis, cat-86 is unexpressed during vegetative growth but expressed during sporulation. The regulation of cat-86 in pPL603 is due to sequences within two restriction fragments, designated P1 and R1, that precede the main coding portion of the gene. The P1 fragment promotes transcription of cat-86 only during sporulation, whereas the adjacent R1 fragment lacks promoter function but contains sequences essential to chloramphenicol inducibility. A second B. pumilus gene, cat-66, was cloned in B. subtilis and is expressed throughout the vegetative growth and sporulation cycle. The cat-66 coding region is preceded by two adjacent restriction fragments designated as P2 and R2. P1 and P2 are identical in size and share 95% conservation of base sequence. R1 and R2 are also identical in size and share 91% conservation of base sequence. Fragment substitution experiments demonstrate that R2 can functionally replace R1. The substitution of P2 for P1 promotes cat-86 expression throughout vegetative growth and sporulation. Analysis of a derivative of pPL603 in which P2 has replaced P1 demonstrates that P2 promotes transcription of cat-86 during vegetative growth and that P2 contains the start site for transcription of cat-86. Thus, P1 and P2 differ strikingly in vegetative promoter function, yet they differ by single-base substitutions at only 11 positions of 203.
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- 1984
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8. Restriction fragments that exert promoter activity during postexponential growth of Bacillus subtilis
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Mongkolsuk, S, Chiang, Y W, Reynolds, R B, and Lovett, P S
- Abstract
Two restriction fragments of Bacillus subtilis DNA were identified which caused the cat-86 gene present on the promoter cloning plasmid pPL703 to be activated predominantly during postexponential growth of host cells. The postexponential increase was observed in both sporulation-positive strains and in a spoOA mutant of B. subtilis. However, the postexponential increase in the cat-86 gene product, chloramphenicol acetyltransferase, was diminished or not observed when the plasmid-containing cells were grown in the presence of excess glucose. The promoter-containing fragment, designated as 33, was mapped to a site on the B. subtilis chromosome adjacent to hisA. The other fragment, 14, mapped to a site adjacent to ctrA. When present on a high-copy vector, both fragments caused a reduction in the sporulation frequency of host cells. Fragment 33 in high copy number conferred on B. subtilis cells three additional phenotypic changes: brown colony color, intracellular inclusions, and, in a protease-deficient mutant, the production of extracellular protease activity. These activities were observed only in postexponential-phase cultures.
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- 1983
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9. Gene expression and physiological role of Pseudomonas aeruginosa methionine sulfoxide reductases during oxidative stress.
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Romsang A, Atichartpongkul S, Trinachartvanit W, Vattanaviboon P, and Mongkolsuk S
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- Animals, Drosophila melanogaster microbiology, Gene Deletion, Methionine Sulfoxide Reductases genetics, Microbial Viability drug effects, Oxidants toxicity, Paraquat toxicity, Pseudomonas aeruginosa drug effects, Pseudomonas aeruginosa pathogenicity, Sodium Hypochlorite toxicity, Survival Analysis, Virulence, Virulence Factors genetics, Gene Expression Regulation, Bacterial, Methionine Sulfoxide Reductases metabolism, Oxidative Stress, Pseudomonas aeruginosa enzymology, Pseudomonas aeruginosa physiology, Stress, Physiological, Virulence Factors metabolism
- Abstract
Pseudomonas aeruginosa PAO1 has two differentially expressed methionine sulfoxide reductase genes: msrA (PA5018) and msrB (PA2827). The msrA gene is expressed constitutively at a high level throughout all growth phases, whereas msrB expression is highly induced by oxidative stress, such as sodium hypochlorite (NaOCl) treatment. Inactivation of either msrA or msrB or both genes (msrA msrB mutant) rendered the mutants less resistant than the parental PAO1 strain to oxidants such as NaOCl and H2O2. Unexpectedly, msr mutants have disparate resistance patterns when exposed to paraquat, a superoxide generator. The msrA mutant had a higher paraquat resistance level than the msrB mutant, which had a lower paraquat resistance level than the PAO1 strain. The expression levels of msrA showed an inverse correlation with the paraquat resistance level, and this atypical paraquat resistance pattern was not observed with msrB. Virulence testing using a Drosophila melanogaster model revealed that the msrA, msrB, and, to a greater extent, msrA msrB double mutants had an attenuated virulence phenotype. The data indicate that msrA and msrB are essential genes for oxidative stress protection and bacterial virulence. The pattern of expression and mutant phenotypes of P. aeruginosa msrA and msrB differ from previously characterized msr genes from other bacteria. Thus, as highly conserved genes, the msrA and msrB have diverse expression patterns and physiological roles that depend on the environmental niche where the bacteria thrive.
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- 2013
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10. Peroxide-sensing transcriptional regulators in bacteria.
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Dubbs JM and Mongkolsuk S
- Subjects
- Bacteria drug effects, Cysteine metabolism, Histidine metabolism, Oxidation-Reduction, Oxidative Stress, Reactive Oxygen Species metabolism, Sodium Hypochlorite metabolism, Stress, Physiological, Bacteria genetics, Bacteria metabolism, Gene Expression Regulation, Bacterial, Peroxides metabolism, Transcription Factors metabolism
- Abstract
The ability to maintain intracellular concentrations of toxic reactive oxygen species (ROS) within safe limits is essential for all aerobic life forms. In bacteria, as well as other organisms, ROS are produced during the normal course of aerobic metabolism, necessitating the constitutive expression of ROS scavenging systems. However, bacteria can also experience transient high-level exposure to ROS derived either from external sources, such as the host defense response, or as a secondary effect of other seemingly unrelated environmental stresses. Consequently, transcriptional regulators have evolved to sense the levels of ROS and coordinate the appropriate oxidative stress response. Three well-studied examples of these are the peroxide responsive regulators OxyR, PerR, and OhrR. OxyR and PerR are sensors of primarily H(2)O(2), while OhrR senses organic peroxide (ROOH) and sodium hypochlorite (NaOCl). OxyR and OhrR sense oxidants by means of the reversible oxidation of specific cysteine residues. In contrast, PerR senses H(2)O(2) via the Fe-catalyzed oxidation of histidine residues. These transcription regulators also influence complex biological phenomena, such as biofilm formation, the evasion of host immune responses, and antibiotic resistance via the direct regulation of specific proteins.
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- 2012
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11. Pseudomonas aeruginosa thiol peroxidase protects against hydrogen peroxide toxicity and displays atypical patterns of gene regulation.
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Somprasong N, Jittawuttipoka T, Duang-Nkern J, Romsang A, Chaiyen P, Schweizer HP, Vattanaviboon P, and Mongkolsuk S
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- Binding Sites, DNA, Bacterial metabolism, Electrophoretic Mobility Shift Assay, Gene Deletion, Gene Expression Profiling, Peroxidase genetics, Peroxidase isolation & purification, Promoter Regions, Genetic, Protein Binding, Pseudomonas aeruginosa drug effects, Pseudomonas aeruginosa genetics, Pseudomonas aeruginosa physiology, Regulon, Gene Expression Regulation, Bacterial, Hydrogen Peroxide metabolism, Hydrogen Peroxide toxicity, Peroxidase metabolism, Pseudomonas aeruginosa enzymology, Repressor Proteins metabolism, Sulfhydryl Compounds metabolism
- Abstract
The Pseudomonas aeruginosa PAO1 thiol peroxidase homolog (Tpx) belongs to a family of enzymes implicated in the removal of toxic peroxides. We have shown the expression of tpx to be highly inducible with redox cycling/superoxide generators and diamide and weakly inducible with organic hydroperoxides and hydrogen peroxide (H(2)O(2)). The PAO1 tpx pattern is unlike the patterns for other peroxide-scavenging genes in P. aeruginosa. Analysis of the tpx promoter reveals the presence of a putative IscR binding site located near the promoter. The tpx expression profiles in PAO1 and the iscR mutant, together with results from gel mobility shift assays showing that purified IscR specifically binds the tpx promoter, support the role of IscR as a transcriptional repressor of tpx that also regulates the oxidant-inducible expression of the gene. Recombinant Tpx has been purified and biochemically characterized. The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. The Δtpx mutant demonstrates differential sensitivity to H(2)O(2) only at moderate concentrations (0.5 mM) and not at high (20 mM) concentrations, suggesting a novel protective role of tpx against H(2)O(2) in P. aeruginosa. Altogether, P. aeruginosa tpx is a novel member of the IscR regulon and plays a primary role in protecting the bacteria from submillimolar concentrations of H(2)O(2).
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- 2012
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12. Novel roles of SoxR, a transcriptional regulator from Xanthomonas campestris, in sensing redox-cycling drugs and regulating a protective gene that have overall implications for bacterial stress physiology and virulence on a host plant.
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Mahavihakanont A, Charoenlap N, Namchaiw P, Eiamphungporn W, Chattrakarn S, Vattanaviboon P, and Mongkolsuk S
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- Bacterial Proteins genetics, Base Sequence, Host-Pathogen Interactions, Molecular Sequence Data, Oxidation-Reduction, Plant Diseases microbiology, Promoter Regions, Genetic, Raphanus microbiology, Stress, Physiological, Transcription Factors genetics, Virulence, Xanthomonas campestris genetics, Xanthomonas campestris pathogenicity, Bacterial Proteins metabolism, Transcription Factors metabolism, Xanthomonas campestris metabolism
- Abstract
In Xanthomonas campestris pv. campestris, SoxR likely functions as a sensor of redox-cycling drugs and as a transcriptional regulator. Oxidized SoxR binds directly to its target site and activates the expression of xcc0300, a gene that has protective roles against the toxicity of redox-cycling compounds. In addition, SoxR acts as a noninducible repressor of its own expression. X. campestris pv. campestris requires SoxR both for protection against redox-cycling drugs and for full virulence on a host plant. The X. campestris model of the gene regulation and physiological roles of SoxR represents a novel variant of existing bacterial SoxR models.
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- 2012
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13. Analyses of the regulatory mechanism and physiological roles of Pseudomonas aeruginosa OhrR, a transcription regulator and a sensor of organic hydroperoxides.
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Atichartpongkul S, Fuangthong M, Vattanaviboon P, and Mongkolsuk S
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- Animals, Bacterial Proteins genetics, Blotting, Northern, Caenorhabditis elegans microbiology, Mutagenesis, Site-Directed, Operon genetics, Promoter Regions, Genetic genetics, Protein Binding genetics, Pseudomonas aeruginosa genetics, Pseudomonas aeruginosa pathogenicity, Repressor Proteins genetics, Reverse Transcriptase Polymerase Chain Reaction, Virulence genetics, Virulence physiology, tert-Butylhydroperoxide pharmacology, Bacterial Proteins metabolism, Gene Expression Regulation, Bacterial drug effects, Gene Expression Regulation, Bacterial genetics, Hydrogen Peroxide pharmacology, Pseudomonas aeruginosa drug effects, Pseudomonas aeruginosa metabolism, Repressor Proteins metabolism
- Abstract
ohrR encodes an organic hydroperoxide sensor and a transcriptional repressor that regulates organic hydroperoxide-inducible expression of a thiol peroxidase gene, ohr, and itself. OhrR binds directly to the operators and represses transcription of these genes. Exposure to an organic hydroperoxide leads to oxidation of OhrR and to subsequent structural changes that result in the loss of the repressor's ability to bind to the operators that allow expression of the target genes. Differential induction of ohrR and ohr by tert-butyl hydroperoxide suggests that factors such as the repressor's dissociation constants for different operators and the chemical nature of the inducer contribute to OhrR-dependent organic hydroperoxide-inducible gene expression. ohrR and ohr mutants show increased and decreased resistance to organic hydroproxides, respectively, compared to a parental strain. Moreover, the ohrR mutant had a reduced-virulence phenotype in the Pseudomonas aeruginosa-Caenorhabditis elegans pathogenicity model.
- Published
- 2010
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14. The catalase-peroxidase KatG is required for virulence of Xanthomonas campestris pv. campestris in a host plant by providing protection against low levels of H2O2.
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Jittawuttipoka T, Buranajitpakorn S, Vattanaviboon P, and Mongkolsuk S
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- Bacterial Proteins genetics, Blotting, Southern, Catalase genetics, Peroxidases genetics, Polymerase Chain Reaction, Raphanus microbiology, Virulence genetics, Xanthomonas campestris drug effects, Xanthomonas campestris enzymology, Xanthomonas campestris pathogenicity, Bacterial Proteins physiology, Catalase metabolism, Hydrogen Peroxide toxicity, Peroxidases metabolism, Virulence drug effects
- Abstract
Xanthomonas campestris pv. campestris katG encodes a catalase-peroxidase that has a role in protecting the bacterium against micromolar concentrations of H(2)O(2). A knockout mutation in katG that causes loss of catalase-peroxidase activity correlates with increased susceptibility to H(2)O(2) and a superoxide generator and is avirulent in a plant model system. katG expression is induced by oxidants in an OxyR-dependent manner.
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- 2009
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15. Functional and expression analyses of the cop operon, required for copper resistance in Agrobacterium tumefaciens.
- Author
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Nawapan S, Charoenlap N, Charoenwuttitam A, Saenkham P, Mongkolsuk S, and Vattanaviboon P
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- Bacterial Proteins genetics, Binding Sites genetics, DNA Footprinting, DNA Transposable Elements genetics, Gene Expression Regulation, Bacterial drug effects, Gene Expression Regulation, Bacterial genetics, Genome, Bacterial genetics, Genome, Bacterial physiology, Mutation, Naphthoquinones pharmacology, Operon genetics, Promoter Regions, Genetic genetics, Reverse Transcriptase Polymerase Chain Reaction, Vitamin K 3 pharmacology, Agrobacterium tumefaciens drug effects, Agrobacterium tumefaciens genetics, Bacterial Proteins physiology, Copper pharmacology, Operon physiology, Trace Elements pharmacology
- Abstract
The copper resistance determinant copARZ, which encodes a CPx-type copper ATPase efflux protein, a transcriptional regulator, and a putative intracellular copper chaperone, was functionally characterized for the phytopathogenic bacterium Agrobacterium tumefaciens. These genes are transcribed as an operon, and their expression is induced in response to increasing copper and silver ion concentrations in a copR-dependent fashion. Analysis of the copARZ promoter revealed a putative CopR binding box located within the spacer of the -35 and -10 promoter motifs. In vitro, purified CopR could specifically bind to the box. The inactivation of the copARZ operon or copZ reduces the level of resistance to copper but not to other metal ions. Also, the copARZ operon mutant shows increased sensitivity to the superoxide generators menadione and plumbagin. In addition, the loss of functional copZ does not affect the ability of copper ions to induce the copARZ promoter, indicating that CopZ is not involved in the copper-sensing mechanism of CopR. Altogether, the results demonstrate a crucial role for the copARZ operon as a component of the copper resistance machinery in A. tumefaciens.
- Published
- 2009
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16. Roles of Agrobacterium tumefaciens RirA in iron regulation, oxidative stress response, and virulence.
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Ngok-Ngam P, Ruangkiattikul N, Mahavihakanont A, Virgem SS, Sukchawalit R, and Mongkolsuk S
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- Agrobacterium tumefaciens genetics, Agrobacterium tumefaciens metabolism, Bacterial Proteins genetics, Gene Expression Regulation, Bacterial, Hydrogen Peroxide metabolism, Iron-Regulatory Proteins genetics, Superoxide Dismutase genetics, Superoxide Dismutase metabolism, Nicotiana microbiology, Virulence, Agrobacterium tumefaciens pathogenicity, Bacterial Proteins metabolism, Iron metabolism, Iron-Regulatory Proteins metabolism, Oxidative Stress, Plant Tumors microbiology
- Abstract
The analysis of genetics and physiological functions of Agrobacterium tumefaciens RirA (rhizobial iron regulator) has shown that it is a transcription regulator and a repressor of iron uptake systems. The rirA mutant strain (NTLrirA) overproduced siderophores and exhibited a highly constitutive expression of genes involved in iron uptake (fhuA, irp6A, and fbpA) compared to that of the wild-type strain (NTL4). The deregulation in the iron control of iron uptake in NTLrirA led to iron overload in the cell, which was supported by the observation that the NTLrirA mutant was more sensitive than wild-type NTL4 to an iron-activated antibiotic, streptonigrin. The NTLrirA mutant was more sensitive than the parental strain to oxidants, including hydrogen peroxide, organic hydroperoxide, and a superoxide generator, menadione. However, the addition of an iron chelator, 2,2'-dipyridyl, reversed the mutant hypersensitivity to H(2)O(2) and organic hydroperoxide, indicating the role of iron in peroxide toxicity. Meanwhile, the reduced level of superoxide dismutase (SodBIII) was partly responsible for the menadione-sensitive phenotype of the NTLrirA mutant. The NTLrirA mutant showed a defect in tumorigenesis on tobacco leaves, which likely resulted from the increased sensitivity of NTLrirA to oxidants and the decreased ability of NTLrirA to induce virulence genes (virB and virE). These data demonstrated that RirA is important for A. tumefaciens during plant-pathogen interactions.
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- 2009
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17. Multiple superoxide dismutases in Agrobacterium tumefaciens: functional analysis, gene regulation, and influence on tumorigenesis.
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Saenkham P, Eiamphungporn W, Farrand SK, Vattanaviboon P, and Mongkolsuk S
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- Agrobacterium tumefaciens drug effects, Agrobacterium tumefaciens growth & development, Gene Deletion, Oxidants pharmacokinetics, Plant Leaves microbiology, Nicotiana microbiology, Virulence genetics, Vitamin K 3 pharmacology, Agrobacterium tumefaciens enzymology, Agrobacterium tumefaciens genetics, Bacterial Proteins genetics, Bacterial Proteins physiology, Gene Expression Regulation, Bacterial, Superoxide Dismutase genetics, Superoxide Dismutase physiology
- Abstract
Agrobacterium tumefaciens possesses three iron-containing superoxide dismutases (FeSods) encoded by distinct genes with differential expression patterns. SodBI and SodBII are cytoplasmic isozymes, while SodBIII is a periplasmic isozyme. sodBI is expressed at a high levels throughout all growth phases. sodBII expression is highly induced upon exposure to superoxide anions in a SoxR-dependent manner. sodBIII is expressed only during stationary phase. Analysis of the physiological function of sods reveals that the inactivation of sodBI markedly reduced levels of resistance to a superoxide generator, menadione. A mutant lacking all three Sod enzymes is the most sensitive to menadione treatment, indicating that all sods contribute at various levels towards the overall menadione resistance level. Sods also have important roles in A. tumefaciens virulence toward a host plant. A sodBI but not a sodBII or sodBIII mutant showed marked reduction in its ability to induce tumors on tobacco leaf discs, while the triple sod null mutant is avirulent.
- Published
- 2007
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18. Physiological and expression analyses of Agrobacterium tumefaciens trxA, encoding thioredoxin.
- Author
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Vattanaviboon P, Tanboon W, and Mongkolsuk S
- Subjects
- Benzene Derivatives pharmacology, Diamide pharmacology, Vitamin K 3 pharmacology, Agrobacterium tumefaciens drug effects, Bacterial Proteins genetics, Gene Expression Regulation, Bacterial, Oxidants pharmacology, Thioredoxins genetics
- Abstract
Exposure of Agrobacterium tumefaciens to menadione, cumene hydroperoxide, and diamide strongly induced trxA expression. The trxA mutant showed a reduction in the aerobic growth rate and plating efficiency and was cytochrome c oxidase negative. Atypically, the mutant has decreased resistance to menadione but an increased H2O2 resistance phenotype.
- Published
- 2007
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19. HpdR is a transcriptional activator of Sinorhizobium meliloti hpdA, which encodes a herbicide-targeted 4-hydroxyphenylpyruvate dioxygenase.
- Author
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Loprasert S, Whangsuk W, Dubbs JM, Sallabhan R, Somsongkul K, and Mongkolsuk S
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- Bacterial Proteins genetics, Bacterial Proteins physiology, DNA Footprinting, DNA, Bacterial metabolism, DNA, Intergenic metabolism, Electrophoretic Mobility Shift Assay, Promoter Regions, Genetic, Protein Binding, Repetitive Sequences, Nucleic Acid, Sinorhizobium meliloti genetics, Trans-Activators metabolism, Transcription, Genetic, 4-Hydroxyphenylpyruvate Dioxygenase biosynthesis, Gene Expression Regulation, Bacterial, Sinorhizobium meliloti physiology, Trans-Activators physiology
- Abstract
Sinorhizobium meliloti hpdA, which encodes the herbicide target 4-hydroxyphenylpyruvate dioxygenase, is positively regulated by HpdR. Gel mobility shift and DNase I footprinting analyses revealed that HpdR binds to a region that spans two conserved direct-repeat sequences within the hpdR-hpdA intergenic space. HpdR-dependent hpdA transcription occurs in the presence of 4-hydroxyphenylpyruvate, tyrosine, and phenylalanine, as well as during starvation.
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- 2007
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20. Agrobacterium tumefaciens soxR is involved in superoxide stress protection and also directly regulates superoxide-inducible expression of itself and a target gene.
- Author
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Eiamphungporn W, Charoenlap N, Vattanaviboon P, and Mongkolsuk S
- Subjects
- Agrobacterium tumefaciens drug effects, Agrobacterium tumefaciens genetics, Agrobacterium tumefaciens metabolism, Bacterial Proteins genetics, Base Sequence, Molecular Sequence Data, Mutation, Promoter Regions, Genetic, Transcription Factors genetics, Transcription, Genetic, Agrobacterium tumefaciens physiology, Bacterial Proteins metabolism, Gene Expression Regulation, Bacterial, Heat-Shock Response, Superoxides pharmacology, Transcription Factors metabolism
- Abstract
Inactivation of Agrobacterium tumefaciens soxR increases sensitivity to superoxide generators. soxR expression is highly induced by superoxide stress and is autoregulated. SoxR also directly regulates the superoxide-inducible expression of atu5152. Taken together, the physiological role of soxR and the mechanism by which it regulates expression of target genes make the A. tumefaciens SoxR system different from other bacterial systems.
- Published
- 2006
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21. Novel organic hydroperoxide-sensing and responding mechanisms for OhrR, a major bacterial sensor and regulator of organic hydroperoxide stress.
- Author
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Panmanee W, Vattanaviboon P, Poole LB, and Mongkolsuk S
- Subjects
- Amino Acid Sequence, Bacterial Proteins chemistry, Bacterial Proteins genetics, Cysteine metabolism, Dimerization, Gene Expression Regulation, Bacterial, Molecular Sequence Data, Mutation, Oxidation-Reduction, Promoter Regions, Genetic, Repressor Proteins chemistry, Repressor Proteins genetics, Sequence Alignment, Transcription Factors chemistry, Transcription Factors genetics, Xanthomonas campestris genetics, Xanthomonas campestris metabolism, Bacterial Proteins metabolism, Hydrogen Peroxide, Repressor Proteins metabolism, Transcription Factors metabolism, Xanthomonas campestris physiology
- Abstract
Xanthomonas campestris pv. phaseoli OhrR belongs to a major family of multiple-cysteine-containing bacterial organic hydroperoxide sensors and transcription repressors. Site-directed mutagenesis and subsequent in vivo functional analyses revealed that changing any cysteine residue to serine did not alter the ability of OhrR to bind to the P1 ohrR-ohr promoter but drastically affected the organic hydroperoxide-sensing and response mechanisms of the protein. Xanthomonas OhrR requires two cysteine residues, C22 and C127, to sense and respond to organic hydroperoxides. Analysis of the free thiol groups in wild-type and mutant OhrRs under reducing and oxidizing conditions indicates that C22 is the organic hydroperoxide-sensing residue. Exposure to organic hydroperoxides led to the formation of an unstable OhrR-C22 sulfenic acid intermediate that could be trapped by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and detected by UV-visible spectral analysis in an oxidized C127S-C131S mutant OhrR. In wild-type OhrR, the cysteine sulfenic acid intermediate rapidly reacts with the thiol group of C127, forming a disulfide bond. The high-performance liquid chromatography-mass spectrometry analysis of tryptic fragments of alkylated, oxidized OhrR and nonreducing polyacrylamide gel electrophoresis analyses confirmed the formation of reversible intersubunit disulfide bonds between C22 and C127. Oxidation of OhrR led to cross-linking of two OhrR monomers, resulting in the inactivation of its repressor function. Evidence presented here provides insight into a new organic hydroperoxide-sensing and response mechanism for OhrRs of the multiple-cysteine family, the primary bacterial transcription regulator of the organic hydroperoxide stress response.
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- 2006
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22. ohrR and ohr are the primary sensor/regulator and protective genes against organic hydroperoxide stress in Agrobacterium tumefaciens.
- Author
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Chuchue T, Tanboon W, Prapagdee B, Dubbs JM, Vattanaviboon P, and Mongkolsuk S
- Subjects
- Agrobacterium tumefaciens drug effects, Bacterial Proteins genetics, Bacterial Proteins metabolism, Gene Expression Regulation, Bacterial, Genes, Bacterial genetics, Heat-Shock Response, Agrobacterium tumefaciens genetics, Bacterial Proteins physiology, Genes, Bacterial physiology, Hydrogen Peroxide pharmacology, Oxidative Stress physiology, Repressor Proteins physiology, Transcription Factors physiology
- Abstract
The genes involved in organic hydroperoxide protection in Agrobacterium tumefaciens were functionally evaluated. Gene inactivation studies and functional analyses have identified ohr, encoding a thiol peroxidase, as the gene primarily responsible for organic hydroperoxide protection in A. tumefaciens. An ohr mutant was sensitive to organic hydroperoxide killing and had a reduced capacity to metabolize organic hydroperoxides. ohr is located next to, and is divergently transcribed from, ohrR, encoding a sensor and transcription regulator of organic hydroperoxide stress. Transcription of both ohr and ohrR was induced by exposure to organic hydroperoxides but not by exposure to other oxidants. This induction required functional ohrR. The results of gel mobility shift and DNase I footprinting assays with purified OhrR, combined with in vivo promoter deletion analyses, confirmed that OhrR regulated both ohrR and ohr by binding to a single OhrR binding box that overlapped the ohrR and ohr promoters. ohrR and ohr are both required for the establishment of a novel cumene hydroperoxide-induced adaptive response. Inactivation or overexpression of other Prx family genes (prx1, prx2, prx3, bcp1, and bcp2) did not affect either the resistance to, or the ability to degrade, organic hydroperoxide. Taken together, the results of biochemical, gene regulation and physiological studies support the role of ohrR and ohr as the primary system in sensing and protecting A. tumefaciens from organic hydroperoxide stress.
- Published
- 2006
- Full Text
- View/download PDF
23. Important role for methionine sulfoxide reductase in the oxidative stress response of Xanthomonas campestris pv. phaseoli.
- Author
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Vattanaviboon P, Seeanukun C, Whangsuk W, Utamapongchai S, and Mongkolsuk S
- Subjects
- Cloning, Molecular, Gene Expression Regulation, Bacterial, Gene Expression Regulation, Enzymologic, Methionine Sulfoxide Reductases, Oxidants metabolism, Xanthomonas campestris growth & development, Oxidative Stress physiology, Oxidoreductases genetics, Oxidoreductases metabolism, Xanthomonas campestris enzymology, Xanthomonas campestris genetics
- Abstract
A methionine sulfoxide reductase gene (msrA) from Xanthomonas campestris pv. phaseoli has unique expression patterns and physiological function. msrA expression is growth dependent and is highly induced by exposure to oxidants and N-ethylmaleimide in an OxyR- and OhrR-independent manner. An msrA mutant showed increased sensitivity to oxidants but only during stationary phase.
- Published
- 2005
- Full Text
- View/download PDF
24. Novel roles of ohrR-ohr in Xanthomonas sensing, metabolism, and physiological adaptive response to lipid hydroperoxide.
- Author
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Klomsiri C, Panmanee W, Dharmsthiti S, Vattanaviboon P, and Mongkolsuk S
- Subjects
- Bacterial Proteins genetics, Bacterial Proteins metabolism, Drug Resistance, Bacterial genetics, Electrophoretic Mobility Shift Assay, Gene Expression Regulation, Bacterial, Linolenic Acids pharmacology, Peroxidases genetics, Peroxidases physiology, Peroxiredoxins, Repressor Proteins genetics, Transcription Factors genetics, Xanthomonas drug effects, Adaptation, Physiological, Bacterial Proteins physiology, Lipid Peroxides pharmacology, Repressor Proteins physiology, Transcription Factors physiology, Xanthomonas physiology
- Abstract
Lipid hydroperoxides are highly toxic to biological systems. Here, the Xanthomonas campestris pv. phaseoli sensing and protective systems against linoleic hydroperoxide (LOOH) were investigated by examining the phenotypes, biochemical and regulatory characteristics of various Xanthomonas mutants in known peroxide resistance pathways. Analysis of LOOH resistance levels indicates that both alkyl hydroperoxide reductase (AhpC) and organic hydroperoxide resistance enzyme (Ohr) have important and nonredundant roles in the process. Nonetheless, inactivation of ohr leads to a marked reduction in LOOH resistance levels. The regulatory characteristics of an ohr mutant add further support to its primary role in LOOH protection. Northern analysis shows that LOOH had differential effects on induction of ahpC and ohr expression with the latter being more sensitive to the inducer. Analysis of the ahpC and ohr promoters confirmed that the LOOH-dependent induction of these promoters is mediated by the transcription regulators OxyR and OhrR, respectively. Using the in vivo promoter assays and the in vitro gel mobility shift assay, we show that LOOH directly oxidized OhrR at the sensing residue Cys-22 leading to its inactivation. In addition, physiological analysis shows that pretreatment of X. campestris pv. phaseoli with a sublethal dose of LOOH induced high levels of resistance to subsequent exposure to lethal concentrations of LOOH. This novel LOOH-induced adaptive response requires a functional ohrR-ohr operon. These data illustrate an important novel physiological role for the ohrR-ohr system in sensing and inactivating lipid hydroperoxides.
- Published
- 2005
- Full Text
- View/download PDF
25. A suppressor of the menadione-hypersensitive phenotype of a Xanthomonas campestris pv. phaseoli oxyR mutant reveals a novel mechanism of toxicity and the protective role of alkyl hydroperoxide reductase.
- Author
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Vattanaviboon P, Whangsuk W, and Mongkolsuk S
- Subjects
- Bacterial Proteins drug effects, Bacterial Proteins metabolism, Catalase drug effects, Catalase metabolism, Gene Expression Regulation, Bacterial, Microbial Sensitivity Tests, Peroxidases drug effects, Peroxiredoxins, Superoxide Dismutase drug effects, Superoxide Dismutase metabolism, Vitamin K 3 toxicity, Mutation, Peroxidases physiology, Vitamin K 3 pharmacology, Xanthomonas campestris drug effects, Xanthomonas campestris physiology
- Abstract
We isolated menadione-resistant mutants of Xanthomonas campestris pv. phaseoli oxyR (oxyR(Xp)). The oxyRR2(Xp) mutant was hyperresistant to the superoxide generators menadione and plumbagin and was moderately resistant to H(2)O(2) and tert-butyl hydroperoxide. Analysis of enzymes involved in oxidative-stress protection in the oxyRR2(Xp) mutant revealed a >10-fold increase in AhpC and AhpF levels, while the levels of superoxide dismutase (SOD), catalase, and the organic hydroperoxide resistance protein (Ohr) were not significantly altered. Inactivation of ahpC in the oxyRR2(Xp) mutant resulted in increased sensitivity to menadione killing. Moreover, high levels of expression of cloned ahpC and ahpF in the oxyR(Xp) mutant complemented the menadione hypersensitivity phenotype. High levels of other oxidant-scavenging enzymes such as catalase and SOD did not protect the cells from menadione toxicity. These data strongly suggest that the toxicity of superoxide generators could be mediated via organic peroxide production and that alkyl hydroperoxide reductase has an important novel function in the protection against the toxicity of these compounds in X. campestris.
- Published
- 2003
- Full Text
- View/download PDF
26. Complex regulation of the organic hydroperoxide resistance gene (ohr) from Xanthomonas involves OhrR, a novel organic peroxide-inducible negative regulator, and posttranscriptional modifications.
- Author
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Sukchawalit R, Loprasert S, Atichartpongkul S, and Mongkolsuk S
- Subjects
- Artificial Gene Fusion, Bacterial Proteins genetics, Base Sequence, DNA, Bacterial, Drug Resistance, Microbial genetics, Genes, Bacterial, Homeostasis, Molecular Sequence Data, Mutagenesis, Nucleic Acid Conformation, Promoter Regions, Genetic, Repressor Proteins genetics, Transcription Factors genetics, Transcription Factors metabolism, Transcription, Genetic, Xanthomonas campestris drug effects, Bacterial Proteins metabolism, DNA-Binding Proteins, Gene Expression Regulation, Bacterial, RNA Processing, Post-Transcriptional, Repressor Proteins metabolism, Xanthomonas campestris genetics, tert-Butylhydroperoxide pharmacology
- Abstract
Analysis of the sequence immediate upstream of ohr revealed an open reading frame, designated ohrR, with the potential to encode a 17-kDa peptide with moderate amino acid sequence homology to the MarR family of negative regulators of gene expression. ohrR was transcribed as bicistronic mRNA with ohr, while ohr mRNA was found to be 95% monocistronic and 5% bicistronic with ohrR. Expression of both genes was induced by tert-butyl hydroperoxide (tBOOH) treatment. High-level expression of ohrR negatively regulated ohr expression. This repression could be overcome by tBOOH treatment. In vivo promoter analysis showed that the ohrR promoter (P1) has organic peroxide-inducible, strong activity, while the ohr promoter (P2) has constitutive, weak activity. Only P1 is autoregulated by OhrR. ohr primer extension results revealed three major primer extension products corresponding to the 5' ends of ohr mRNA, and their levels were strongly induced by tBOOH treatment. Sequence analysis of regions upstream of these sites showed no typical Xanthomonas promoter. Instead, the regions can form a stem-loop secondary structure with the 5' ends of ohr mRNA located in the loop section. The secondary structure resembles the structure recognized and processed by RNase III enzyme. These findings suggest that the P1 promoter is responsible for tBOOH-induced expression of the ohrR-ohr operon. The bicistronic mRNA is then processed by RNase III-like enzymes to give high levels of ohr mRNA, while ohrR mRNA is rapidly degraded.
- Published
- 2001
- Full Text
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27. OhrR is a repressor of ohrA, a key organic hydroperoxide resistance determinant in Bacillus subtilis.
- Author
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Fuangthong M, Atichartpongkul S, Mongkolsuk S, and Helmann JD
- Subjects
- Amino Acid Sequence, Bacillus subtilis genetics, Bacillus subtilis metabolism, Bacterial Proteins genetics, Base Sequence, Binding Sites, DNA, Bacterial, Drug Resistance, Microbial genetics, Gene Expression Regulation, Bacterial, Molecular Sequence Data, Repressor Proteins genetics, Transcription, Genetic, Bacillus subtilis drug effects, Bacterial Proteins physiology, Hydrogen Peroxide pharmacology, Repressor Proteins physiology
- Abstract
Bacillus subtilis displays a complex adaptive response to the presence of reactive oxygen species. To date, most proteins that protect against reactive oxygen species are members of the peroxide-inducible PerR and sigma(B) regulons. We investigated the function of two B. subtilis homologs of the Xanthomonas campestris organic hydroperoxide resistance (ohr) gene. Mutational analyses indicate that both ohrA and ohrB contribute to organic peroxide resistance in B. subtilis, with the OhrA protein playing the more important role in growing cells. Expression of ohrA, but not ohrB, is strongly and specifically induced by organic peroxides. Regulation of ohrA requires the convergently transcribed gene, ohrR, which encodes a member of the MarR family of transcriptional repressors. In an ohrR mutant, ohrA expression is constitutive, whereas expression of the neighboring ohrB gene is unaffected. Selection for mutant strains that are derepressed for ohrA transcription identifies a perfect inverted repeat sequence that is required for OhrR-mediated regulation and likely defines an OhrR binding site. Thus, B. subtilis contains at least three regulons (sigma(B), PerR, and OhrR) that contribute to peroxide stress responses.
- Published
- 2001
- Full Text
- View/download PDF
28. A Xanthomonas alkyl hydroperoxide reductase subunit C (ahpC) mutant showed an altered peroxide stress response and complex regulation of the compensatory response of peroxide detoxification enzymes.
- Author
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Mongkolsuk S, Whangsuk W, Vattanaviboon P, Loprasert S, and Fuangthong M
- Subjects
- Gene Expression Regulation, Bacterial, Hydrogen Peroxide pharmacology, Mutagenesis, Peroxidases genetics, Peroxiredoxins, Repressor Proteins genetics, Transcription Factors genetics, Xanthomonas drug effects, Xanthomonas genetics, Catalase metabolism, DNA-Binding Proteins, Oxidative Stress, Peroxidases metabolism, Repressor Proteins metabolism, Transcription Factors metabolism, Xanthomonas enzymology
- Abstract
Alkyl hydroperoxide reductase subunit C (AhpC) is the catalytic subunit responsible for alkyl peroxide metabolism. A Xanthomonas ahpC mutant was constructed. The mutant had increased sensitivity to organic peroxide killing, but was unexpectedly hyperresistant to H(2)O(2) killing. Analysis of peroxide detoxification enzymes in this mutant revealed differential alteration in catalase activities in that its bifunctional catalase-peroxidase enzyme and major monofunctional catalase (Kat1) increased severalfold, while levels of its third growth-phase-regulated catalase (KatE) did not change. The increase in catalase activities was a compensatory response to lack of AhpC, and the phenotype was complemented by expression of a functional ahpC gene. Regulation of the catalase compensatory response was complex. The Kat1 compensatory response increase in activity was mediated by OxyR, since it was abolished in an oxyR mutant. In contrast, the compensatory response increase in activity for the bifunctional catalase-peroxidase enzyme was mediated by an unknown regulator, independent of OxyR. Moreover, the mutation in ahpC appeared to convert OxyR from a reduced form to an oxidized form that activated genes in the OxyR regulon in uninduced cells. This complex regulation of the peroxide stress response in Xanthomonas differed from that in other bacteria.
- Published
- 2000
- Full Text
- View/download PDF
29. Mutations in oxyR resulting in peroxide resistance in Xanthomonas campestris.
- Author
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Mongkolsuk S, Whangsuk W, Fuangthong M, and Loprasert S
- Subjects
- Drug Resistance, Microbial, Gene Expression Regulation, Bacterial, Mutagenesis, Peroxidases genetics, Peroxidases metabolism, Peroxiredoxins, Repressor Proteins genetics, Repressor Proteins metabolism, Transcription Factors genetics, Transcription Factors metabolism, Xanthomonas campestris genetics, Xanthomonas campestris metabolism, DNA-Binding Proteins, Hydrogen Peroxide pharmacology, Repressor Proteins physiology, Transcription Factors physiology, Xanthomonas campestris drug effects
- Abstract
A spontaneous Xanthomonas campestris pv. phaseoli H(2)O(2)-resistant mutant emerged upon selection with 1 mM H(2)O(2). In this report, we show that growth of this mutant under noninducing conditions gave high levels of catalase, alkyl hydroperoxide reductase (AhpC and AhpF), and OxyR. The H(2)O(2) resistance phenotype was abolished in oxyR-minus derivatives of the mutant, suggesting that elevated levels and mutations in oxyR were responsible for the phenotype. Nucleotide sequence analysis of the oxyR mutant showed three nucleotide changes. These changes resulted in one silent mutation and two amino acid changes, one at a highly conserved location (G197 to D197) and the other at a nonconserved location (L301 to R301) in OxyR. Furthermore, these mutations in oxyR affected expression of genes in the oxyR regulon. Expression of an oxyR-regulated gene, ahpC, was used to monitor the redox state of OxyR. In the parental strain, a high level of wild-type OxyR repressed ahpC expression. By contrast, expression of oxyR5 from the X. campestris pv. phaseoli H(2)O(2)-resistant mutant and its derivative oxyR5G197D with a single-amino-acid change on expression vectors activated ahpC expression in the absence of inducer. The other single-amino-acid mutant derivative of oxyR5L301R had effects on ahpC expression similar to those of the wild-type oxyR. However, when the two single mutations were combined, as in oxyR5, these mutations had an additive effect on activation of ahpC expression.
- Published
- 2000
- Full Text
- View/download PDF
30. Construction and physiological analysis of a Xanthomonas mutant to examine the role of the oxyR gene in oxidant-induced protection against peroxide killing.
- Author
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Mongkolsuk S, Sukchawalit R, Loprasert S, Praituan W, and Upaichit A
- Subjects
- Aerobiosis, Bacterial Proteins genetics, Catalase biosynthesis, Gene Expression Regulation, Enzymologic, Kinetics, Oxidative Stress, Oxidoreductases biosynthesis, Peroxiredoxins, Plasmids, Repressor Proteins biosynthesis, Superoxide Dismutase metabolism, Time Factors, Transcription Factors biosynthesis, Xanthomonas campestris drug effects, Xanthomonas campestris genetics, DNA-Binding Proteins, Gene Expression Regulation, Bacterial, Hydrogen Peroxide pharmacology, Oxidants pharmacology, Peroxidases, Repressor Proteins genetics, Transcription Factors genetics, Vitamin K pharmacology, Xanthomonas campestris physiology
- Abstract
We constructed and characterized a Xanthomonas campestris pv. phaseoli oxyR mutant. The mutant was hypersensitive to H2O2 and menadione killing and had reduced aerobic plating efficiency. The oxidants' induction of the catalase and ahpC genes was also abolished in the mutant. Analysis of the adaptive responses showed that hydrogen peroxide-induced protection against hydrogen peroxide was lost, while menadione-induced protection against hydrogen peroxide was retained in the oxyR mutant. These results show that X. campestris pv. phaseoli oxyR is essential to peroxide adaptation and revealed the existence of a novel superoxide-inducible peroxide protection system that is independent of OxyR.
- Published
- 1998
- Full Text
- View/download PDF
31. Identification and characterization of a new organic hydroperoxide resistance (ohr) gene with a novel pattern of oxidative stress regulation from Xanthomonas campestris pv. phaseoli.
- Author
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Mongkolsuk S, Praituan W, Loprasert S, Fuangthong M, and Chamnongpol S
- Subjects
- Amino Acid Sequence, Base Sequence, Gene Expression Regulation, Bacterial, Genetic Complementation Test, Molecular Sequence Data, Mutation, Sequence Alignment, Sequence Homology, Amino Acid, Bacterial Proteins genetics, Genes, Bacterial genetics, Genes, Regulator genetics, Oxidative Stress, Xanthomonas campestris genetics
- Abstract
We have isolated a new organic hydroperoxide resistance (ohr) gene from Xanthomonas campestris pv. phaseoli. This was done by complementation of an Escherichia coli alkyl hydroperoxide reductase mutant with an organic hydroperoxide-hypersensitive phenotype. ohr encodes a 14.5-kDa protein. Its amino acid sequence shows high homology with several proteins of unknown function. An ohr mutant was subsequently constructed, and it showed increased sensitivity to both growth-inhibitory and killing concentrations of organic hydroperoxides but not to either H2O2 or superoxide generators. No alterations in sensitivity to other oxidants or stresses were observed in the mutant. ohr had interesting expression patterns in response to low concentrations of oxidants. It was highly induced by organic hydroperoxides, weakly induced by H2O2, and not induced at all by a superoxide generator. The novel regulation pattern of ohr suggests the existence of a second organic hydroperoxide-inducible system that differs from the global peroxide regulator system, OxyR. Expression of ohr in various bacteria tested conferred increased resistance to tert-butyl hydroperoxide killing, but this was not so for wild-type Xanthomonas strains. The organic hydroperoxide hypersensitivity of ohr mutants could be fully complemented by expression of ohr or a combination of ahpC and ahpF and could be partially complemented by expression ahpC alone. The data suggested that Ohr was a new type of organic hydroperoxide detoxification protein.
- Published
- 1998
- Full Text
- View/download PDF
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