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The recA gene of Mycobacterium tuberculosis is unusual in that it is expressed from two promoters, one of which, P1, is DNA damage inducible independently of LexA and RecA, while the other, P2, is regulated by LexA in the classical way (E. O. Davis, B. Springer, K. K. Gopaul, K. G. Papavinasasundaram, P. Sander, and E. C. Bottger, Mol. Microbiol. 46:791-800, 2002). In this study we characterized these two promoters in more detail. Firstly, we localized the promoter elements for each of the promoters, and in so doing we identified a mutation in each promoter which eliminates promoter activity. Interestingly, a motif with similarity to Escherichia coli [[sigma].sup.70] -35 elements but located much closer to the -10 element is important for optimal expression of P1, whereas the sequence at the -35 location is not. Secondly, we found that the sequences flanking the promoters can have a profound effect on the expression level directed by each of the promoters. Finally, we examined the contribution of each of the promoters to recA expression and compared their kinetics of induction following DNA damage.

Research was conducted to examine the role of protein Cra in transcription of the icd gene. In vitro transcription method revealed that in addition to its main promoter a second promoter was contained in the icd control region. Tests conducted on specific point mutations in the alpha subunit of RNA polymerase demonstrated that various RNAP-DNA contacts have an important role to play in the transcription of the icd gene.