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Regulation of the Expression of Cell Wall Stress Stimulon Member Gene msrA1 in Methicillin-Susceptible or -Resistant Staphylococcus aureus. Roger Pechous, 2004.Genome-wide transcriptional profiling studies of the response of Staphylococcus aureus to cell wall-active antibiotics have led to the discovery of a cell wall stress stimulon of genes induced by these agents . msrA1, encoding methionine sulfoxide reductase, is a highly induced member gene of this stimulon . In the present study we show that msrA1 induction by oxacillin is common to all methicillin-susceptible strains studied but did not occur in two homogeneous and two heterogeneous methicillin-resistant strains . However, msrA1 was induced by vancomycin and/or D-cycloserine in methicillin-resistant strains . Lysozyme and lysostaphin treatment did not induce msrA1 expression . Oxacillin-induced msrA1 expression was enhanced by ca . 30% in a SigB+ derivative (SH1000) of the SigB-defective RN450 (NCTC 8325-4) strain . msrA1 expression was not affected in mutants in the global regulatory systems agr and sar . Glycerol monolaurate, an inhibitor of signal transduction, inhibited the oxacillin-induced transcription of msrA1 and other cell wall stress stimulon member genes, vraS and dnaK . These observations suggest that the cell wall stress stimulon is induced by inhibition of the process of peptidoglycan biosynthesis, and the inhibitory effects of glycerol monolaurate indicate that gene expression is dependent on a signal transduction pathway . Inversions over the Terminus Region in Salmonella and Escherichia coli: IS200s as the Sites of Homologous Recombination Inverting the Chromosome of Salmonella enterica Serovar Typhi. Suneetha Alokam, 2002.Genomic rearrangements (duplications and inversions) in enteric bacteria such as Salmonella enterica serovar Typhimurium LT2 and Escherichia coli K12 are frequent (10-3 to 10-5) in culture, but in wild-type strains these genomic rearrangements seldom survive . However, inversions commonly survive in the terminus of replication (TER) region, where bidirectional DNA replication terminates; nucleotide sequences from S . enterica serovar Typhimurium LT2, S . enterica serovar Typhi CT18, E . coli K12, and E . coli O157:H7 revealed genomic inversions spanning the TER region . Assuming that S . enterica serovar Typhimurium LT2 represents the ancestral genome structure, we found an inversion of 556 kb in serovar Typhi CT18 between two of the 25 IS200 elements and an inversion of about 700 kb in E . coli K12 and E . coli O157:H7 . In addition, there is another inversion of 500 kb in E . coli O157:H7 compared with E . coli K12 . PCR analysis confirmed that all S . enterica serovar Typhi strains tested, but not strains of other Salmonella serovars, have an inversion at the exact site of the IS200 insertions . We conclude that inversions of the TER region survive because they do not significantly change replication balance or because they are part of the compensating mechanisms to regain chromosome balance after it is disrupted by insertions, deletions, or other inversions . Localization of the Vegetative Cell Wall Hydrolases LytC, LytE, and LytF on the Bacillus subtilis Cell Surface and Stability of These Enzymes to Cell Wall-Bound or Extracellular Proteases. Hiroki Yamamoto, 2003.LytF, LytE, and LytC are vegetative cell wall hydrolases in Bacillus subtilis . Immunofluorescence microscopy showed that an epitope-tagged LytF fusion protein (LytF-3xFLAG) in the wild-type background strain was localized at cell separation sites and one of the cell poles of rod-shaped cells during vegetative growth . However, in a mutant lacking both the cell surface protease WprA and the extracellular protease Epr, the fusion protein was observed at both cell poles in addition to cell separation sites . This suggests that LytF is potentially localized at cell separation sites and both cell poles during vegetative growth and that WprA and Epr are involved in LytF degradation . The localization pattern of LytE-3xFLAG was very similar to that of LytF-3xFLAG during vegetative growth . However, especially in the early vegetative growth phase, there was a remarkable difference between the shape of cells expressing LytE-3xFLAG and the shape of cells expressing LytF-3xFLAG . In the case of LytF-3xFLAG, it seemed that the signals in normal rod-shaped cells were stronger than those in long-chain cells . In contrast, the reverse was found in the case of LytE-3xFLAG . This difference may reflect the dependence on different sigma factors for gene expression . The results support and extend the previous finding that LytF and LytE are cell-separating enzymes . On the other hand, we observed that cells producing LytC-3xFLAG are uniformly coated with the fusion protein after the middle of the exponential growth phase, which supports the suggestion that LytC is a major autolysin that is not associated with cell separation .
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