SEQUENCES IN THE -35-REGION OF ESCHERICHIA-COLI RPOS-DEPENDENT GENES PROMOTE TRANSCRIPTION BY E-SIGMA(S)

sigma(S) is an alternate sigma factor which functions with RNA polymer ase to activate transcription of genes that are involved in a number o f stress responses, including stationary-phase survival and osmoprotec tion. The similarity of the sigma(S) protein to sigma(D) (Escherichia coli's major sigma factor) in the regions thought to recognize and bin d promoter sequences suggests that sigma(S) - and sigma(D)-associated RNA polymerases recognize promoter DNA in a similar manner. However, n o promoter recognition sequence for sigma(S) holoenzyme (E sigma(S)) h as been identified. An apparent conservation of cytosine nucleotides w as noted in the -35 region of several sigma(S)-dependent promoters. Si te directed mutagenesis and reporter gene fusions were used to investi gate the importance of the -35 cytosine nucleotides for sigma(S)-depen dent transcription. Substitution of cytosine nucleotides for thymidine at the -35 site of the sigma(D)-dependent proU promoter effectively a bolished transcription by E sigma(D) but allowed E sigma(S) to direct transcription from the mutant promoter. Inclusion of the sigma(D) cons ensus -10 hexamer strengthened transcription by E sigma(S), demonstrat ing that both E sigma(D) and E sigma(S) can recognize the same -10 seq uences. Conversely, replacement of -35 site cytosine nucleotides with thymidine in the sigma(S)-dependent osmY promoter reduced transcriptio n by E sigma(S) and increased transcription by E sigma(D). Our data su ggest that DNA sequences in the -35 region function as part of a discr iminator mechanism to shift transcription between E sigma(D) and E sig ma(S).