EFFECTS OF H-NS AND POTASSIUM GLUTAMATE ON SIGMA(S)-DIRECTED AND SIGMA(70)-DIRECTED TRANSCRIPTION IN-VITRO FROM OSMOTICALLY REGULATED P1 AND P2 PROMOTERS OF PROU IN ESCHERICHIA-COLI

We have used supercoiled DNA templates in this study to demonstrate th at transcription in vitro from the P1 and P2 promoters of the osmoresp onsive proU operon of Escherichia coli is preferentially mediated by t he sigma(S)- and sigma(70)-bearing RNA polymerase holoenzymes, respect ively. Addition of potassium glutamate resulted in the activation of t ranscription from both P1 and P2 and also led to a pronounced enhancem ent of sigma(S) selectivity at the P1 promoter. Transcription from P2, and to a lesser extent from P1, was inhibited by the nucleoid protein H-NS but only in the absence of potassium glutamate. This study valid ates the existence of dual promoters with dual specificities for proU transcription. Our results also support the proposals that potassium, which is known to accumulate in cells grown at high osmolarity, is at least partially responsible for effecting the in vivo induction of pro U transcription and that it does so through two mechanisms, directly b y the activation of RNA polymerase and indirectly by the relief of rep ression imposed by H-NS.