Regulation of RNA polymerase sigma subunit synthesis in Escherichia coli: Intracellular levels of four species of sigma subunit under various growth conditions

By a quantitative Western immunoblot analysis, the intracellular levels of two principal sigma subunits, sigma(70) (sigma(D), the rpoD gene product) and sigma(38) (sigma(S), the rpoS gene product), and of two minor sigma subunits, sigma(54) (sigma(N), the rpoN gene product) and sigma(28) (sigma(F), the rpoF gene product), were determined in two Escherichia coli strains, W3110 and MC4100, The results indicated that the levels of sigma(54) and sigma(28) are maintained at 10 and 50%, respectively, of the level of sigma(70) in both strains growing at both exponential and stationary phases, but in agreement with the previous measurement for strain MC4100 (M. Jishage and A. Ishihama, J. Bacteriol. 177:6832-6835, 1995), the level of sigma(38) was undetectable at the exponential growth phase but increased to 30% of the level of sigma(70) at the stationary phase, Stress-coupled change in the intracellular level was observed for two cr subunits: (i) the increase in sigma(38) level and the decrease in sigma(28) level upon exposure to heat shock at the exponential phase and (ii) the increase in sigma(38) level under high-osmolality conditions at both the exponential and stationary phases.