Transcription-repair coupling factor is involved in carbon catabolite repression of the Bacillus subtilis hut and gnt operons

A Bacilius subtilis mutant that partially relieves carbon catabolite repression (CCR) of the hut operon was isolated by transposon mutagenesis. Characterization of this mutant revealed that the transposon had inserted into the gene, mfd, that encodes transcription-repair coupling factor. The Mfd protein is known to promote strand-specific DNA repair by displacing RNA polymerase stalled at a nucleotide lesion and directing the (A)BC excinuclease to the RNA damage site. A set of transcriptional lacZ fusions was used to demonstrate that the mfd mutation relieves CCR of hut and gnt expression at the cis-acting ore sequences located downstream of the transcriptional start site but does not affect CCR at sites located at the promoters. CCR of the amyE and bglPH genes, which contain ore sequences that overlap their promoters, is not altered by the mfd mutation. These results support a model in which the Mfd protein displaces RNA polymerase stalled at downstream ore sites that function as transcriptional roadblocks and reveal a new role for Mfd in cellular physiology.