This domain is found associated with an N-terminal cyclic nucleotide-binding domain (IPR000595) and two CBS domains (IPR000644). This domain, normally represents the C-terminal region, is uncharacterised; however, it seems to be similar to the nucleotidyltransferase domain (IPR002934), conserving the DXD motif, which strongly suggests that proteins containing this domain are also nucleotidyltransferases.