Differential inhibition of transcription from sigma70- and sigma32-dependent promoters by rifampicin.

Rifampicin is an antibiotic which binds to the beta subunit of prokaryotic RNA polymerases and prevents initiation of transcription. It was found previously that production of heat shock proteins in Escherichia coli cells after a shift from 30 degrees C to 43 degrees C is not completely inhibited by this antibiotic. Here we demonstrate that while activity of a pL-lacZ fusion (pL is a sigma70-dependent promoter) in E. coli cells is strongly inhibited by rifampicin, a p(groE)-lacZ fusion, whose activity is dependent on the sigam32 factor, retains significant residual activity even at relatively high rifampicin concentrations. Differential sensitivity to this antibiotic of RNA polymerase holoenzymes containing either the sigma70 or the sigma32 subunit was confirmed in vitro. Since the effects of an antibiotic that binds to the beta subunit can be modulated by the presence of either the sigma70 or the sigma32 subunit in the holoenzyme, it is tempting to speculate that binding of various sigma factors to the core of RNA polymerase results in different conformations of particular holoenzymes, including changes in the core enzyme.