PROMOTER RECOGNITION BY BACILLUS-SUBTILIS SIGMA(W) - AUTOREGULATION AND PARTIAL OVERLAP WITH THE SIGMA(X) REGULON

The Bacillus subtilis genome encodes at least 17 distinct sigma factor s, including seven members of the extracytoplasmic function (ECF) subf amily, We have investigated the expression and regulation of the ECF a factor encoded by the sigW gene. A sigma(W)-dependent promoter (P-W) precedes sigW, demonstrating that this transcription factor is positiv ely autoregulated. Expression of sigW is regulated by both growth phas e and medium composition. Maximal expression is attained in early-stat ionary-phase cells grown in rich medium. We previously reported that s igW mutants have elevated transcription of some sigma(X)-controlled ge nes, and we now report that the converse is also true: in a sigX mutan t, P-W is derepressed during logarithmic growth. Thus, these two regul ons are mutually antagonistic. Reconstituted sigma(W) holoenzyme faith fully recognizes the P-W preceding sigW but does not recognize the P-X promoter preceding the sigX gene. Autoregulation of sigX is also high ly specific: sigma(X) holoenzyme initiates transcription from P-X but recognizes P-W poorly if at all. In contrast, several promoters that a re at least partially under sigma(X) control are active with both the sigma(X) and sigma(W) holoenzymes in vitro. This finding supports the suggestion that the sigma(W) and sigma(X) regulons overlap. Sequence c omparisons suggest that promoters recognized by these two a factors ha ve similar -35 elements but are distinguished by different base prefer ences at two key positions within the -10 element.