CHARACTERIZATION OF THE LOCUS ENCODING THE [NI-FE] SULFHYDROGENASE FROM THE ARCHAEON PYROCOCCUS-FURIOSUS - EVIDENCE FOR A RELATIONSHIP TO BACTERIAL SULFITE REDUCTASES

The hydBGDA genes, which encode the four subunits beta, gamma, delta a nd alpha of the [Ni-Fe] hydrogenase from the archaeon Pyrococcus furio sus, have been isolated and sequenced using a PCR/IPCR-based strategy. From the sequence analysis it appears that the four structural genes are tightly linked and organized in a single transcription unit. The h ydD and hydA gene products are related to the small and the large subu nits of several archaeal and eubacterial [Ni-Fe] hydrogenases with an overall degree of sequence relatedness ranging from 35% to 50% (identi ty + similarity). In particular, the amino acid sequence motifs involv ed in the accommodation of nickel and iron-sulfur clusters are conserv ed. In addition, the database search revealed that the hydB and hydG g ene products are homologous to the asrA- and asrB-encoded subunits of the sulfite reductase enzyme from Salmonella typhimurium. This is part icularly interesting in view of the recent finding that the P. furiosu s hydrogenase appears to be a bifunctional enzyme endowed with both pr oton- and sulfur-reducing activities.