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Clp-HSP100 ATPases are a widespread family of ubiquitous proteins that occur in both prokaryotes and eukaryotes and play important roles in the folding of newly synthesized proteins and refolding of aggregated proteins. They have also been shown to participate in the virulence of several pathogens, including Listeria monocytogenes. Here, we describe a member of the Clp-HSP100 family of L. monocytogenes that harbors all the characteristics of the ClpB subclass, which is absent in the closely related gram-positive model organism, Bacillus subtilis. Transcriptional analysis of clpB revealed a heat shock-inducible [[sigma].sup.A]-type promoter. Potential binding sites for the CtsR regulator of stress response were identified in the promoter region. In vivo and in vitro approaches were used to show that expression of clpB is repressed by CtsR, a finding indicating that clpB is a novel member of the L. monocytogenes CtsR regulon. We showed that CIpB is involved in the pathogenicity of L. monocytogenes since the [DELTA]clpB mutant is significantly affected by virulence in a murine model of infection; we also demonstrate that this effect is apparently not due to a defect in general stress resistance. Indeed, CIpB is not involved in tolerance to heat, salt, detergent, puromycin, or cold stress, even though its synthesis is inducible by heat shock. However, ClpB was shown to play a role in induced thermotolerance, allowing increased resistance of L. monocytogenes to lethal temperatures. This work gives the first example of a clpB gene directly controlled by CtsR and describes the first role for a ClpB protein in induced thermotolerance and virulence in a gram-positive organism.

Research has been conducted on the crystal structure of the tyrosyl-tRNA synthetase C-terminal domain from Bacillus stearothermophilus. The characterization of its conformational state is discussed.

The physical mapping of the chromosome of the Mycobacterium bovis (Mb)BCG Pasteur classical vaccine strain was conducted to determine the presence of segments that are different from the chromosomes of Mb and M. tuberculosis (Mt). The genomes of Mb BCG Pasteur and Mb exhibited colinearity due to the presence of extensively conserved genes and similar restriction fragments. The Mb BCG Pasteur chromosome also contains a restriction length polymorphism that is similar to the chromosome structure of Mb.

Research has been conducted on Streptococcus agalactiae heat-shock protein ClpP. Results demonstrate that this protein plays important role in heat-induced growth arrest in S. agalactiae.

Research was conducted to examine the involvement of the Mycobacterium tuberculosis katG gene in the protection of DNA-repair-deficient Escherichia coli mutants against DNA-damaging agents. Since there are no defined M. tuberculosis DNA-repair mutants, heterologous hosts were used in the study. Results based on the preliminary screening of an M. tuberculosis genomic DNA library on EMS indicate that the katG gene may be involved in DNA repair.