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J. Bacteriol., May 1996, 2785-2793, Vol 178, No. 10
Copyright © 1996, American Society for Microbiology

Sequences in the -35 region of Escherichia coli rpoS-dependent genes promote transcription by E sigma S

A Wise, R Brems, V Ramakrishnan and M Villarejo
Section of Microbiology, University of California, Davis 95616, USA. aawise@ucdavis.edu

sigma S is an alternate sigma factor which functions with RNA polymerase to activate transcription of genes that are involved in a number of stress responses, including stationary-phase survival and osmoprotection. The similarity of the sigma S protein to sigma D (Escherichia coli's major sigma factor) in the regions thought to recognize and bind promoter sequences suggests that sigma S- and sigma D-associated RNA polymerases recognize promoter DNA in a similar manner. However, no promoter recognition sequence for sigma S holoenzyme (E sigma S) has been identified. An apparent conservation of cytosine nucleotides was noted in the -35 region of several sigma S- dependent promoters. Site-directed mutagenesis and reporter gene fusions were used to investigate the importance of the -35 cytosine nucleotides for sigma S-dependent transcription. Substitution of cytosine nucleotides for thymidine at the -35 site of the sigma D- dependent proU promoter effectively abolished transcription by E sigma D but allowed E sigma S to direct transcription from the mutant promoter. Inclusion of the sigma D consensus -10 hexamer strengthened transcription by E sigma S, demonstrating that both E sigma D and E sigma S can recognize the same -10 sequences. Conversely, replacement of -35 site cytosine nucleotides with thymidine in the sigma S- dependent osmY promoter reduced transcription by E sigma S and increased transcription by E sigma D. Our data suggest that DNA sequences in the -35 region function as part of a discriminator mechanism to shift transcription between E sigma D and E sigma S.


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