Molecular characterization of the promoter of osmY, an rpoS-dependent gene

The osmY gene, which encodes a periplasmic protein with an apparent M(r) of 22,000, is induced by both osmotic and growth phase signals. We demonstrate here that osmY expression is regulated at the level of transcription and that transcription initiates 242 nucleotides upstream of the osmY open reading frame. Relative to the transcriptional start site, 5' deletions up to -36 did not inhibit osmY expression. 3' deletions that extended into the untranslated leader region affected the overall level of osmY::lacZ expression but did not affect inducibility. 5' and 3' deletions that extended past the transcriptional start region essentially abolished osmY expression, suggesting that there is a single promoter region. A putative promoter was identified, and its -10 region, TATATT, closely resembles the sigma 70 consensus -10 sequence, TATAAT. However, we show that osmY is not absolutely dependent on a functional sigma 70 for its expression. Since osmY expression does require rpoS (R. Hengge-Aronis, R. Lange, N. Henneberg, and D. Fischer, J. Bacteriol. 175:259-265, 1993), which encodes a stationary-phase sigma factor, sigma S (K. Tanaka, Y. Takayanagi, N. Fujita, A. Ishihama, and H. Takahashi, Proc. Natl. Acad. Sci. USA 90:3511-3515, 1993), E sigma S may be the form of RNA polymerase responsible for transcription of osmY.