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Journal of Bacteriology, June 2002, p. 3167-3175, Vol. 184, No. 12
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.12.3167-3175.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

An N-Terminally Truncated RpoS ({sigma}S) Protein in Escherichia coli Is Active In Vivo and Exhibits Normal Environmental Regulation Even in the Absence of rpoS Transcriptional and Translational Control Signals

K. Rajkumari1 and J. Gowrishankar1,2*

Centre for Cellular and Molecular Biology, Hyderabad 500 007,1 Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500 076, India2

Received 10 August 2001/ Accepted 6 March 2002

RpoS ({sigma}S) in Escherichia coli is a stationary-phase-specific primary sigma factor of RNA polymerase which is 330 amino acids long and belongs to the eubacterial {sigma}70 family of proteins. Conserved domain 1.1 at the N-terminal end of {sigma}70 has been shown to be essential for RNA polymerase function, and its deletion has been shown to result in a dominant-lethal phenotype. We now report that a {sigma}S variant with a deletion of its N-terminal 50 amino acids ({sigma}S{Delta}1-50), when expressed in vivo either from a chromosomal rpoS::IS10 allele (in rho mutant strains) or from a plasmid-borne arabinose-inducible promoter, is as proficient as the wild type in directing transcription from the proU P1 promoter; at three other {sigma}S-dependent promoters that were tested (osmY, katE, and csiD), the truncated protein exhibited a three- to sevenfold reduced range of activities. Catabolite repression at the csiD promoter (which requires both {sigma}S and cyclic AMP [cAMP]-cAMP receptor protein for its activity) was also preserved in the strain expressing {sigma}S{Delta}1-50. The intracellular content of {sigma}S{Delta}1-50 was regulated by culture variables such as growth phase, osmolarity, and temperature in the same manner as that described earlier for {sigma}S, even when the truncated protein was expressed from a template that possessed neither the transcriptional nor the translational control elements of wild-type rpoS. Our results indicate that, unlike that in {sigma}70, the N-terminal domain in {sigma}S may not be essential for the protein to function as a sigma factor in vivo. Furthermore, our results suggest that the induction of {sigma}S-specific promoters in stationary phase and during growth under conditions of high osmolarity or low temperature is mediated primarily through the regulation of {sigma}S protein degradation.

* Corresponding author. Mailing address: Centre for DNA Fingerprinting and Diagnostics, ECIL Rd., Nacharam, Hyderabad 500 076, India. Phone: 91-40-7155609. Fax: 91-40-7155610. E-mail: shankar{at}www.cdfd.org.in.

Journal of Bacteriology, June 2002, p. 3167-3175, Vol. 184, No. 12
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.12.3167-3175.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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