Expression of the microcin C51 operon in Escherichia coli cells is activated during cell entry into the stationary growth phase and depends on the σS subunit of RNA polymerase (RpoS). The null rpoS mutations retained the residual expression level of the transcriptional Pmcc-lac fusion, which indicates that other sigma subunit can participate in the regulation of transcription of the microcin C51 operon. Data presented in this work show that the overproduction of σ70 in rpoS cells diminished the level of Pmcc-lac expression, as in wild-type cells, which seems to be the consequence of competition between sigma factors for a limited number of core RNA polymerase molecules. In the presence of the rpoD800 mutation that renders σ70 temperature-sensitive, expression of Pmcc-lac was not induced in the phase of delayed culture growth at nonpermissive temperature, which indicates that σ70 is indispensable for microcin operon expression. Point substitutions in the –10 Pmcc region, leading to the formation of 5′-TGaTATAAT-3′ site, enhanced promoter activity but did not affect the relationship between Pmcc-lac transcription and growth phase, σS, and the activator protein CRP. The activator protein CRP was shown to bind a DNA fragment containing the TGTGA(AATGAA)TCTAT site in the –59.5 bp position relative to the start site of transcription. Mutation in the ssr1 gene encoding 6S RNA did not disturb Pmcc-lac expression; these results indicate that 6S RNA does not participate in the regulation of microcin C51 operon expression.
Russian Journal of Genetics – Springer Journals
Published: Dec 14, 2004
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