All living cells are constantly exposed to chemical and physical agents that have the ability to alter the primary structure of DNA. Thus, it should be expected that all organisms appears to have mechanisms for the removal or repair of this damage. During the last thirty years, a great of effort has been placed on trying to elucidate the various DNA repair mechanisms that exist as well as the relationship of these repair systems to cell survival, mutagenesis, genetic recombination, DNA replication, carcinogenesis, toxicology, differentiation and development. The Gram positive spore-forming bacterium Bacillus subtilis a model for the study of the interactions of DNA repair with differentiation. Specifically, aspects of this SOS system are spontaneously activated when B. subtilis differentiates into its competent state. The present study concentrates on the molecular mechanisms that regulate the damage induction and the competence specific induction of din(DNA damage inducible) genes and of the recA gene. Operator/promoter regions from these genes have been isolated and sequenced. Regulatory elements, transcription start sites have been tentatively identified. The preliminary data suggest the existence of complex regulatory networks involved in the regulation of some of these genes, especially the recA promoter. Using the appropriate techniques of molecular biology and genetics, such as S1 nuclease protection, gel mobility shift assays, Western Blots, DNA sequencing, cloning mutational analysis, polymerase chain reaction, transposon inactivation, etc, the following questions will be addressed: 1) What DNA sequences are essential for the damage inducible expression of the recA gene; and 2) what DNA sequences are essential for the competence specific induction of the recA gene? %%% This award should provide detailed insight into how bacterial cells regulate an important aspect of their response to environmental stress.
