TRANSCRIPTIONAL REGULATION OF THE PREVOTELLA-RUMINICOLA RECA GENE

The regulation of the recA gene expression in the obligately anaerobic rumen bacterium Prevotella ruminicola was investigated by monitoring the recA-specific transcript level. P. ruminicola recA forms a monocis tronic unit, but no SOS-box sequences resembling those of Escherichia coli or Bacillus subtilis can be identified upstream of the recA codin g region. At the same time, we observed a fivefold increase in the lev el of recA mRNA in response to DNA damaging agents: mitomycin C and me thyl methanesulfonate, as well as under conditions of oxidative stress . No induction was detected when growth of P. ruminicola was arrested by shifting to acidic (pH 4.8) conditions. Primer extension experiment revealed the three very close transcriptional start sites for recA. T he putative -10 and -35 RNA polymerase binding regions were proposed o n the basis of transcript mapping. These regions bear very little simi larity to the E. coli (sigma(70)) and B. subtilis (sigma(A)) consensus sequences, as well as to the recognition sites of other minor a-facto rs. Transcript mapping experiments in E. coli expressing P. ruminicola recA confirmed that the transcription machineries of these two bacter ia recognize completely different regulatory sequences on the template to initiate transcription. Preliminary DNase I footprinting analysis data revealed that the region of imperfect dyad symmetry (AATTATAATCAA TTATAAAT) found between the putative -10 region and the translation in itiation codon may serve as an SOS-box-like regulatory sequence in P. ruminicola. This sequence bears no similarity to the known SOS-box seq uences and, in particular, to that of E. coli and other Gram-negative bacteria.