The Streptomyces glaucescens TcmR protein represses transcription of the divergently oriented tcmR and tcmA genes by binding to an intergenic operator region.

Preliminary evidence has been presented by Guilfoile and Hutchinson (J. Bacteriol. 174:3651-3658, 1992) suggesting that the Streptomyces glaucescens TcmR protein is a transcriptional repressor. Here, we extend that work by showing that transcription of the S. glaucescens tcmA gene is inducible by tetracenomycin C and that inactivation of the tcmR gene results in constitutive transcription of the tcmA gene. Gel retardation studies show that the TcmR protein binds to the tcmA-tcmR intergenic region in vitro and that this binding is inhibited by tetracenomycin C. Footprinting experiments demonstrate that the TcmR protein binds to an operator region that encompasses both the tcmA and the tcmR promoters. This genetic and biochemical evidence strongly supports the model of the TcmR protein acting as a repressor in inhibiting transcription of both the tcmA and the tcmR genes, in much the same way that TetR from Tn10 inhibits transcription of tetA and tetR.