Nucleotide sequences of two hydrogenase-related genes (hypA and hypB) from Bradyrhizobium japonicum, one of which (hypB) encodes an extremely histidine-rich region and guanine nucleotide-binding domains.

Sequencing of a 1359-bp (NruI-AccI) DNA fragment located approximately 5.2 kb downstream from the end of the hydrogenase structural genes of Bradyrhizobium japonicum revealed two open reading frames designated hypA and hypB, encoding polypeptides with predicted molecular masses of 12.3 and 32.8 kDa, respectively. Both hypA and hypB showed strong homology with other genes in hydrogenase-containing bacteria. Two 'C-X-X-C' motifs were contained in the deduced amino acid sequence of hypA, a motif that is present in all known products homologous to HypA. The deduced product of hypB contains an area remarkably rich in histidine residues at the N-terminus (24 histidines within a 39 amino acid stretch). The deduced HypB also contains GTP-binding domains. We postulate that the product of hypB is involved in nickel binding and accumulation, and may utilize energy (GTP) to mobilize nickel for its subsequent incorporation into hydrogenase.