Two extracytoplasmic function sigma subunits, sigma(E) and sigma(FecI) of Escherichia coli: Promoter selectivity and intracellular levels

The promoter selectivity of two extracytoplasmic function (ECF) subfamily s igma subunits, sigma(E) (sigma(24)) and sigma(FecI) (sigma(18)), of Escheri chia coli RNA polymerase was analyzed by using an in vitro transcription sy stem and various promoters. The E sigma(E) holoenzyme recognized only the k nown cognate promoters, rpoEP2, rpoHP3, and degP, and the E sigma(FecI) rec ognized only one known cognate promoter, fecA. The strict promoter recognit ion properties of sigma(E) and sigma(FecI) are similar to those of other mi nor a subunits. Transcription by E sigma(E) and E sigma(FecI) was enhanced by high concentrations of glutamate, as in the case of other minor a subuni ts. The optimum temperature for transcription by E sigma(FecI) was low, aro und 25 degrees C, apparently in agreement with the high rate of iron seques tration by E. coli at low temperatures. By quantitative Western blot analys is, the intracellular levels of sigma(E) and sigma(FecI) in the uninduced s teady-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 mu g 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 m ajor sigma(70) subunit.