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Porphyromonas gingivalis, an obligately anaerobic bacterium, is implicated as a major pathogen in the development and progression of chronic periodontitis. Although expression of several virulence factors of the bacterium has been found to be affected by environmental stress such as entrance into the stationary growth phase and heat, there is relatively little information on the mechanisms that may operate in the bacterium in response to environmental stress. In this study, a novel protein (UstA) was investigated that was initially identified following two-dimensional gel analysis. Expression of UstA was upregulated in stationary phase or by exposure to atmospheric oxygen. N-terminal sequencing and database analysis with the P. gingivalis genome sequence revealed that the UstA-encoding gene (ustA) was located upstream of a homologue of the usp gene encoding the universal stress protein on the chromosome. The ustA gene appeared to be transcribed in a monocistronic fashion, as revealed by primer extension and Northern blot analysis. To elucidate the role of UstA in the bacterium, chromosomal mutants carrying a disruption of the ustA gene were constructed. The ustA mutant grew slower than the wild-type parent strain in rich medium, resulting in a lower yield in stationary phase. Furthermore, in this mutant, expression levels of the P. gingivalis homologues of superoxide dismutase, thiol peroxidase and thioredoxin were markedly higher than those in the wild-type, especially in stationary phase. The ustA mutant was more resistant to diamide, a thiol-specific oxidant, than the wild-type. In addition, the ustA mutation suppressed hypersensitivities of the oxyR mutant to diamide, metronidazole and mitomycin C. These results suggest that UstA may play a significant role in oxidative stress responses in the bacterium.

Research has been conducted on Porphyromonas gingivalis nonpigmented mutant. The construction of this mutant has been carried out via the use of transposon mutagenesis and the results indicate that the mutant possesses transposon DNA at the porR gene involved in the cell surface polysaccharide biosynthesis.

A study concerning the preparation and the X-ray structure of the linked-bisphosphido dipalladium(II) complexes is presented. The employment of the linked-bisphosphido groups as a ligand is discussed.

Arginine-specific cysteine proteinase (RGP) acts as a processing proteinase for maturation of fimbrilin in Porphyromonas gingivalis. RGP also appears to be involved in the maturation of some cell surface proteins. Double mutations in the rgpA and rgpB genes that code for RGP results in accumulation of a 75-kDa protein, one of the main outer membrane proteins of P. gingivalis. Immunoblot analysis of cell extracts shows that the double mutant produces two immunoreactive proteins with 45 kDA and 43 kDa molecular masses, representing the precursor and mature forms of fimbrilin.

The viability of superoxide dismutase (SoD) deficient Porphyromonas gingivalis mutant is reduced when exposed to air. P. gingivalis is an anaerobe containing SoD with extreme aerotolerance. SoD mutant activity is studied by disturbing the SoD encoding gene by a SoD mutant. The results indicate the necessity of SoD for resistivity to air exposure.

The Streptococcus mutans gene coding for superoxide dismutase (SOD) was cloned and characterized. Sequence analysis showed that SOD is a manganese-SOD. Insertion mutagenesis of the sod gene resulted in the complete loss of SOD activity, indicating that the isolated gene codes for the sole SOD in S. mutans. This conclusion was confirmed by Southern hybridization experiments using an oligonucleotide probe corresponding to a conserved sod sequence.

Techniques to fabricate thick multi-layer 4H-SiC epitaxial wafers were studied for very high-voltage p- and n-channel insulated gate bipolar transistors (IGBTs). Multi-layer epitaxial growth, including a thick p- drift layer (~180?μm), was performed on a 4H-SiC n+ substrate to form a p-IGBT structure. For an n-IGBT structure, an inverted growth process was employed, in which a thick n- drift layer (~180?μm) and a thick p++ injector layer (>55?μm) were epitaxially grown. The epitaxial growth conditions were modified to attain a low defect density, a low doping concentration, and a long carrier lifetime in the drift layers. Reduction of the forward voltage drop was attempted by using carrier lifetime enhancement processes, specifically, carbon ion implantation/annealing and thermal oxidation/annealing or hydrogen annealing. Simple PiN diodes were fabricated to demonstrate the effective conductivity modulation in the thick drift layers. The forward voltage drops of the PiN diodes with the p- and n-IGBT structures promise to obtain the extremely low-loss and very high-voltage IGBTs. The change in wafer shape during the processing of the very thick multi-layer 4H-SiC is also discussed. [ABSTRACT FROM AUTHOR]

Microtubules are among bio-polymers providing vital functions in dynamic cellular processes. Artificial organization of these bio-polymers is a requirement for transferring their native functions into device applications. Using electrophoresis, we achieve an accumulation of microtubules along a metallic glass (Pd42.5Cu30Ni7.5P20) microwire in solution. According to an estimate based on migration velocities of microtubules approaching the wire, the electrophoretic mobility of microtubules is around 10-12 m2/Vs. This value is four orders of magnitude smaller than the typical mobility reported previously. Fluorescence microscopy at the individual-microtubule level shows microtubules aligning along the wire axis during the electric field-induced migration. Caseintreated electrodes are effective to reversibly release trapped microtubules upon removal of the external field. An additional result is the condensation of secondary filamentous structures from oriented microtubules. [ABSTRACT FROM AUTHOR]