Bacillus subtilis σ^B is regulated by a binding protein (RsbW) that blocks its association with core RNA polymerase

Authors

Andrew K. Benson, University of Nebraska-LincolnFollow
William G. Haldenwang, University of Texas Health Science - San Antonio

Document Type

Article

Date of this Version

1993

Comments

Published in Proc. Natl. Acad. Sci. USA (1993) Vol. 90, pp. 2330-2334

Abstract

σ^B is a secondary σ factor of Bacillus subtilis. RNA polymerase containing cr transcribes a subset of genes that are expressed after heat shock or the onset of the stationary phase of growth. Three genes (rsbV, rsbW, and rsbX), cotranscribed with the σ^B structural gene (sigB), regulate o dependent gene expression. RsbW is the primary inhibitor of this system with the other gene products acting upstream of RsbW in the σ^B regulatory pathway. Evidence is now presented that RsbW inhibits σ^B-dependent transcription by binding to crB and blocking the formation of a σ^B-containing RNA polymerase holoenzyme. Antibodies specific for either RsbW or σ^B will coprecipitate both proteins from crude cell extracts. This is not due to the presence of both proteins on RNA polymerase. Western blot analysis of B. subtilis extracts that had been fractionated by gel-fitration chromatography revealed a single peak of RsbW that did not coelute with RNA polymerase and two peaks of σ^B protein: one that eluted with RNA polymerase and a second that overlapped the fractions that contained RsbW. Reconstitution experiments were performed in which partially purified σ^B and RsbW were added to core RNA polymerase and tested for their ability to influence the transcription of a σ^B-dependent promoter (ctc) in vitro. RsbW efficiently blocked σ^B-dependent transcription but only if it was incubated with σ^B prior to the addition of the core enzyme.