Coordinate positive regulation of genes encoding [NiFe] hydrogenases in Methanococcus voltae

Two transcription units encoding selenium-free [NiFe] hydrogenases in Methanococcus voltae are transcribed only upon selenium deprivation. Their products replace or complement selenocysteine-containing isoenzymes. The transcription units are linked by a 453-bp intergenic region, and are subject to both positive and negative transcriptional regulation. The mechanism of positive regulation was studied in detail. Mutations in identical 11-bp putative activator recognition sites close to each promoter showed that each site is involved in the activation of both promoters. Sequence-specific DNA-affinity chromatography yielded a 55-kDa protein which specifically recognized the 11-bp sequence. We consider this protein to be a transcriptional activator for both transcription units.