SEQUENCE-ANALYSIS AND INTERPOSON MUTAGENESIS OF THE HUPT GENE, WHICH ENCODES A SENSOR PROTEIN INVOLVED IN REPRESSION OF HYDROGENASE SYNTHESIS IN RHODOBACTER-CAPSULATUS

The hupT gene, which represses hydrogenase gene expression in the purp le photosynthetic bacterium Rhodobacter capsulatus, has been identifie d and sequenced. The nucleotide sequence of hupT and of the contiguous downstream open reading frame, hupU, is reported. The HupT protein of 456 amino acids (48,414 Da) has sequence similarity with the FixL, Dc tB, NtrB, and ArcB proteins and is predicted to be a soluble sensor ki nase. Insertional inactivation of the hupT gene led to deregulation of transcriptional control, so that the hydrogenase structural operon hu pSLC became overexpressed in cells grown anaerobically or aerobically. The HupT- mutants were complemented in trans by a plasmid containing an intact copy of the hupT gene. The hupU open reading frame, capable of encoding a protein of 84,879 Da, shared identity with [NiFe]hydroge nase subunits; the strongest similarity was observed with the periplas mic hydrogenase of Desulfovibrio baculatus.