This CD represents a family of iron-molybdenum cluster-binding proteins that includes NifB, NifX, and NifY, all of which are involved in the synthesis of an iron-molybdenum cofactor (FeMo-co) that binds the active site of the dinitrogenase enzyme. This domain is a predicted small-molecule-binding domain (SMBD) with an alpha/beta fold that is present either as a stand-alone domain (e.g. NifX and NifY) or fused to another conserved domain (e.g. NifB) however, its function is still undetermined.The SCOP database suggests that this domain is most similar to structures within the ribonuclease H superfamily. This conserved domain is represented in two of the three major divisions of life (bacteria and archaea).