| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 96 === ASTRACT
Two-component signal transduction system (TCS) is the major signal transduction and regulation system in bacteria. Cellular functions such as metabolic activity, stress responses, drug resistance, competence, and virulence all are regulated by TCS. The VicRK (also known as YycFG) TCS, encoded by vic operon, is widely identified in Gram-positive bacteria, and its impact in cell wall biogenesis, and virulence gene expression has been demonstrated in various streptococcal species, Staphylococcus aureus, and Bacillus subtilis. Recent study in our laboratory revealed that a vicRKX operon is present in Streptococcus salivarius and the expression of this operon has been confirmed by RT-PCR. To analyze the expression of vic operon in S. salivarius, a promoter-chloramphenicol resistance gene fusion (pvic-cat) was constructed and integrated into the lacZ locus in this study. The promoter activities in cells grown at different conditions were examined by measuring CAT activity. The expression of pvic was regulated by both growth stages and culture pH, with lower expression in cells grown in the stationary stages and under acidic pH. Transcription start site was located 62 bp 5’ to the ATG. An extended -10 promoter sequence was found in the corresponding region and a regulator binding sequence proposed for S. pneumoniae VicR was located at -132 bp. Furthermore, the amount of vicR-specific message, measured by RT-PCR, was up-regulated in the vicK-deficient strain comparing to the wild-type strain grown under the same condition. These results suggested that the expression of pvic was negatively autoregulated by phosphorylated VicR. Functional analysis indicated that an intact vicK, but not the vicX, was essential for optimal oxidative stress responses and biofilm formation. Thus, it is likely that Vic TCS is involved in a global regulatory circuit in S. salivarius.
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