CLONING AND NUCLEOTIDE-SEQUENCE OF THE PSRA GENE OF WOLINELLA-SUCCINOGENES POLYSULFIDE REDUCTASE

The polysulphide reductase (formerly sulphur reductase) of Wolinella succinogenes is a component of the phosphorylative electron transport system with polysulphide as the terminal acceptor. Using an antiserum raised against the major subunit (PsrA, 85 kDa) of the enzyme, the corresponding gene (psrA) was cloned from a lambda-gene bank. The N-terminal amino acid sequence of PsrA mapped within the psrA gene product, which also contained an apparent signal peptide. Downstream of the psrA gene two more open reading frames (psrB and psrC) were found. The three genes may form a transcriptional unit with the transcription start site in front of psrA. The three genes were present only once on the genome. PsrA is a hydrophilic protein homologous to the largest subunits of six prokaryotic molybdoenzymes. PsrB is predicted to be hydrophilic, to contain ferredoxin-like cysteine clusters and to be homologous to the smaller hydrophilic subunits of four molybdoenzymes. PsrC is predicted to be a hydrophobic protein that could possibly serve as the membrane anchor of the enzyme.