GenR, an IclR-type regulator, activates and represses the transcription of gen genes involved in 3-hydroxybenzoate and gentisate catabolism in Corynebacterium glutamicum.

The genes required for 3-hydroxybenzoate and gentisate catabolism in Corynebacterium glutamicum are closely clustered in three operons. GenR, an IclR-type regulator, can activate the transcription of genKH and genDFM operons in response to 3-hydroxybenzoate and gentisate, and it can repress its own expression. Footprinting analyses demonstrated that GenR bound to four sites with different affinities. Two GenR-binding sites (DFMn01 and DFMn02) were found to be located between positions --41 and --84 upstream of the --35 and --10 regions of the genDFM promoter, which was involved in positive regulation of genDFM transcription. The GenR binding site R-KHn01 (located between positions --47 and --16) overlapped the --35 region of the genKH promoter sequence and is involved in positive regulation of its transcription. The binding site R-KHn02, at which GenR binds to its own promoter, was found within a footprint extending from position --44 to --67. It appeared to be involved in negative regulation of the activity of the genR promoter. A consensus motif with a 5-bp imperfect palindromic sequence [ATTCC-N(7(5))-GGAAT] was identified among all four GenR binding sites and found to be necessary to GenR regulation through site-directed mutagenesis. The results reveal a new regulatory function of the IclR family in the catabolism of aromatic compounds.