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Factors influencing preferential utilization of RNA polymerase containing sigma-38 in stationary-phase gene expression in Escherichia coli.

In order to understand the molecular basis of selective expression of stationary-phase genes by RNA polymerase containing sigma38 (Esigma38) in Escherichia coli, we examined transcription from the stationary-phase promoters, katEP, bolAP, hdeABP, csgBAP, and mcbP, in vivo and in vitro. Although these promoters are preferentially recognized in vivo by Esigma38, they are transcribed in vitro by both Esigma38 and Esigma70 containing the major exponential sigma, sigma70. In the presence of high concentrations of glutamate salts, however, only Esigma38 was able to efficiently transcribe from these promoters, which supports the concept that the promoter selectivity of sigma38-containing RNA polymerase is observed only under specific reaction conditions. The examination of 6S RNA, which is encoded by the ssr1 gene in vivo, showed that it reduced Esigma70 activity during the stationary phase, but this reduction of activity did not result in the elevation of Esigma38 activity. Thus, the preferential expression of stationary-phase genes by Esigma38 is unlikely the consequence of selective inhibition of Esigma70 by 6S RNA.