REGULATION OF RNA-POLYMERASE-SIGMA SUBUNIT SYNTHESIS IN ESCHERICHIA-COLI - INTRACELLULAR LEVELS OF SIGMA(70) AND SIGMA(38)

The intracellular levels of two principal sigma subunits, sigma(70) (sigma(D), the rpoD gene product) acid sigma(38) (sigma(S), the rpoS gene product), in Escherichia coli MC4100 were determined by a quantitative Western immunoblot analysis, Results indicate that the level of sigma(70) is maintained at 50 to 80 fmol per mu g of total proteins throughout the transition from the exponential growth phase to the stationary phase, while the level of sigma(38) protein is below the detection level at the exponential growth phase but increases to 30% of the level of sigma(70) when cell growth stops to enter into the stationary phase, Beside the stationary phase, the increase in sigma(38) level was observed in two cases: exposure to heat shock at the exponential phase and osmotic shock at the stationary phase.