Nucleotide sequence of the genetic loci encoding subunits of Bradyrhizobium japonicum uptake hydrogenase

An indispensable part of the hydrogen-recycling system in Bradyrhizobium japonicum is the uptake hydrogenase, which is composed of 34.5- and 65.9-kDa subunits. The gene encoding the large subunit is located on a 5.9-kilobase fragment of the H2-uptake-complementing cosmid pHU52 [Zuber, M., Harker, A.R., Sultana, M.A. & Evans, H.J. (1986) Proc. Natl. Acad. Sci. USA 83, 7668-7672]. We have now determined that the structural genes for both subunits are present on this fragment. Two open reading frames are present that correspond in size and deduced amino acid sequence to the hydrogenase subunits, except that the small-subunit coding region contains a leader peptide of 46 amino acids. The two genes are separated by a 32-nucleotide intergenic region and likely constitute an operon. Comparison of the deduced amino acid sequences of the B. japonicum genes with those from Desulfovibrio gigas, Desulfovibrio baculatus, and Rhodobacter capsulatus indicates significant sequence identity.