Characterization of type 3 SOS phenomena in Bacillus subtilis.

摘要

Previously, SOS phenomena similar to that of Escherichia coli have also been identified in Bacillus subtilis. Using Tn917 transposon containing a promoterless lacZ gene, B. subtilis din (DNA damage inducible) genes have been isolated, cloned, and sequenced (reviewed by Yasbin et al., 1993). Computer analysis of the din gene promoter sequences has resulted in the identification of a consensus sequence GAAC-N4-GTTC (Cheo box). Deletion and point mutation analysis have demonstrated that this Cheo box and regions adjacent to it are required for the repression of the SOS system in B. subtilis. Furthermore, these din genes are also induced during the development of competence (competence is defined as the ability of the cells to take-up and internalize foreign DNA). Specifically, dinB and dinC require a functional RecA for competence induction, while recA is independent of a functional RecA for its induction during competence. Searches of the recA promoter for possible competence regulation elements have identified a ComK consensus sequence (ComK is a transcription factor required for the induction of late competence genes). Deletion analysis has shown that the ComK consensus is required for the RecA-independent competence induction of recA.;In this dissertation, din gene expression was reexamined in a genetic background proficient for DNA repair, and previously a type 1 SOS gene dinA was identified to be a type 3 SOS gene. Furthermore, a library of point mutations covering the Cheo box region of the recA gene was established to study the requirements of a functional SOS box in B. subtilis. The data suggest that the actual DNA structure of the Cheo box region, as well as the Cheo box consensus, might be required for the repression of the din genes. They also suggest that the SOS box region could be involved in a type of positive regulation during DNA damage induction of the recA gene. Deletion and point mutation constructs were also used to study the competence induction of the recA gene. The data suggest that an inter-relationship between the upstream site for competence factor and the basal transcription machinery is required for the competence specific induction of the recA gene. The data presented in this thesis support the hypothesis that the adaption of the SOS response during differentiation might help B. subtilis cells cope with environmental change and increase the chance of the cell to survive in a stressful environment.