PROMOTER SELECTIVITY CONTROL OF ESCHERICHIA-COLI RNA-POLYMERASE BY IONIC-STRENGTH - DIFFERENTIAL RECOGNITION OF OSMOREGULATED PROMOTERS BY E-SIGMA(D) AND E-SIGMA(S) HOLOENZYMES

Transcription in vitro of two osmoregulated promoters, for the Escherichia coli osmB and osmY genes, was analysed using two species of RNA polymerase holoenzyme reconstituted from purified core enzyme and either sigma(D) (sigma(70) the major sigma in exponentially growing cells) or sigma(S) (sigma(38), the principal sigma at stationary growth phase). Under conditions of low ionic strength, the osmB and osmY promoters were transcribed by both E sigma(D) and E sigma(S). Addition of up to 400 mM potassium glutamate (K glutamate), mimicking the intracellular ionic conditions under hyperosmotic stress, specifically enhanced transcription at these promoters by E sigma(S) but inhibited that by E sigma(D). At similar high concentrations of potassium chloride (KCI), however, initiation at both these promoters was virtually undetectable. These data suggest that the RNA polymerase, E sigma(S), itself can sense osmotic stress by responding to changes in intracellular K glutamate concentrations and altering its promoter selectivity in order to recognize certain osmoregulated promoters.