Identification and sequencing of a cytochrome P450 gene cluster from Bradyrhizobium japonicum

Sequencing of a region from Bradyrhizobium japonicum previously shown to encode for cytochromes P450 revealed a cluster of three complete P450 genes (CYP112, CYP114, and CYP117) plus a partial P450 gene fragment (CYP115P). Present also are five additional open reading frames. The close positioning of the genes suggests that they comprise an operon. Although the biochemical function of the gene products is uncertain, the similarities to other genes suggests an operon involved in terpenoid synthesis. ORF3 has similarity to a [3Fe-4S] ferredoxin from Streptomyces griseolus. ORF4 has strong similarity to members of the short chain alcohol dehydrogenase family, including sterol dehydrogenases from enteric bacteria and to some plant 3-oxoacyl-(acyl carrier protein) reductases. ORF6 has strong similarity to prenyl transferases, including dimethylallyltranstransferase from Escherichia coli. ORF7 bears some similarity to plant genes for ent-kaurene synthase (a precursor of gibberellins), and to bacterial squalene-hopene cyclases. ORF8 has some similarity to a Streptomyces gene for synthesis of the cyclic sesquiterpene pentalenene. The 5' end of the mRNA transcript is 38-39 nucleotides downstream from the center of a motif that bears sequence homology to bacterial fnr promoters. A gus operon fusion to the promoter was expressed anaerobically and symbiotically 6-10-fold greater than aerobically.