DETERMINATION OF DNA-SEQUENCES REQUIRED FOR REGULATED MYCOBACTERIUM-TUBERCULOSIS RECA EXPRESSION IN RESPONSE TO DNA-DAMAGING AGENTS SUGGESTS THAT 2 MODES OF REGULATION EXIST

The recA gene of Mycobacterium tuberculosis has previously been cloned and sequenced (E. O. Davis, S. G. Sedgwick, and M. J. Colston, J. Bac teriol. 173:5653-5662, 1991). In this study, the expression of this ge ne was shown to be inducible in response to various DNA-damaging agent s by using a transcriptional fusion to the reporter gene encoding chlo ramphenicol acetyltransferase. A segment of DNA around 300 bp upstream of the coding region was shown to be required for expression. However , primer extension analysis indicated that the transcriptional start s ites were 47 and 93 bp upstream of the translation initiation codon. S equence motifs with homology to two families of Escherichia coli promo ters but also with significant differences were located near these pro posed transcription start sites. The differences from the E. coli cons ensus patterns would explain the previously described lack of expressi on of the M. tuberculosis recA gene from its own promoter in E. coil. In addition, the M. tuberculosis LexA protein was shown to bind specif ically to a sequence, GAAC-N4-GTTC, overlapping one of these putative promoters and homologous to the Bacillus subtilis Cheo box involved in the regulation of SOS genes. The region of DNA 300 bp upstream of the recA gene was shown not to contain a promoter, suggesting that it fun ctions as an upstream activator sequence.