Products of the iron-molybdenum cofactor-specific biosynthetic genes, nifE and nifN, are structurally homologous to the products of the nitrogenase molybdenum-iron protein genes, nifD and nifK.

The genes from Azotobacter vinelandii, which are homologous to the iron-molybdenum cofactor biosynthetic genes, nifE and nifN, from Klebsiella pneumoniae, have been cloned and sequenced. These genes comprise a single transcription unit and are located immediately downstream from the nitrogenase structural gene cluster (nifHDK). DNA sequence analysis has revealed that the products of the nifE and nifN genes contain considerable homology when compared with the nifD (MoFe protein alpha subunit) and the nifK (MoFe protein beta subunit) gene products, respectively. These striking sequence homologies indicate a structural and functional relationship between a proposed nifEN product complex and the nitrogenase MoFe protein as well as imply an ancestral relationship between these gene clusters. The isolation and characterization of strains which contain deletions within the nifEN gene cluster demonstrate a role for these products in iron-molybdenum cofactor biosynthesis in A. vinelandii.