The complete sequences of the dsrA and dsrB genes coding for the alpha- and beta-subunits, respectively, of the sulphite reductase enzyme in Desulfovibrio desulfuricans were determined. Analyses of the amino acid sequences indicated a number of serohaem/Fe4S4 binding consensus sequences whilst predictive secondary structure analysis revealed a similar pattern of alpha-helix and beta-strand structures between the two subunits which was indicative of gene duplication.