Two Extracytoplasmic Function Sigma Subunits, ς E and ς FecI , of Escherichia coli : Promoter Selectivity and Intracellular Levels

Abstract

ABSTRACT The promoter selectivity of two extracytoplasmic function (ECF) subfamily ς subunits, ς E (ς 24 ) and ς FecI (ς 18 ), of Escherichia coli RNA polymerase was analyzed by using an in vitro transcription system and various promoters. The Eς E holoenzyme recognized only the known cognate promoters, rpoE P2, rpo HP3, and degP , and the Eς FecI recognized only one known cognate promoter, fecA . The strict promoter recognition properties of ς E and ς FecI are similar to those of other minor ς subunits. Transcription by Eς E and Eς FecI was enhanced by high concentrations of glutamate, as in the case of other minor ς subunits. The optimum temperature for transcription by Eς FecI was low, around 25°C, apparently in agreement with the high rate of iron sequestration by E. coli at low temperatures. By quantitative Western blot analysis, the intracellular levels of ς E and ς FecI in the uninduced steady-state culture of E. coli W3110 (type A) were determined to be 0.7 to 2.0 and 0.1 to 0.2 fmol per μg of total proteins (or 3 to 9 and 0.4 to 0.9 molecules per cell), respectively, and less than 1% of the level of the major ς 70 subunit.