Regulation of divergent transcription from the uvrA-ssb promoters in Sinorhizobium meliloti

The Sinorhizobium meliloti uvrA gene was isolated by complementation of a Rhodobacter sphaeroides UvrA- mutant. DNA sequencing of the region upstream of the S. meliloti uvrA gene reveals the presence of the ssb gene in the opposite transcriptional orientation. PCR-mediated mutagenesis demonstrated that expression of these two genes is inducible by DNA damage, and depends, in both cases, on the direct repeat GTTCN7GTTC (cited according to the direction of uvrA transcription). Comparison of the sequences of recA and uvrA promoters from different bacterial species of the alpha group of the Proteobacteria has identified the direct repeat GTTCYYKTTTTGTTC as the SOS box in this phylogenetic group.