INCREASED DISTAL GENE-TRANSCRIPTION BY THE ELONGATION-FACTOR RFAH, A SPECIALIZED HOMOLOG OF NUSG

The Escherichia coil RfaH protein is required for the expression of op erons directing synthesis and export of the toxin haemolysin, the lipo polysaccharide core, and the F-factor sex pilus. Mutation of rfaH incr eases transcriptional polarity along all three operons. By demonstrati ng strong RfaH-dependent suppression of transcription polarity in vitr o, we have established RfaH as a novel transcriptional activator, and we reveal that RfaH is a homologue of the essential protein NusG that modulates general transcriptional pausing and termination in prokaryot es. Full transcription of the distal genes from an upstream promoter r equired RfaH and the 5' cis-acting ops element, both in vivo and in vi tro. In vivo the requirement for the ops element was suppressed by ove rexpressing RfaH, and in vitro the presence of ops lowered the concent ration of RfaH required to stimulate transcript elongation. We suggest that RfaH directs transcript elongation in an analogous way to NusG, but does so in a subset of bacterial operons primarily engaged in the production of extracellular components required for virulence and fert ility.