This domain is located at the C-terminal region of ISPD (isoprenoid synthase domain containing protein, EC:2.7.7.40), Pfam:PF01128. Structural homologs can be found in two distinct alpha/beta protein families including the seven-stranded NAD(P) (H)-dependent short-chain dehydrogenases/reductases and five-stranded response regulator proteins involved in bacterial sensing systems [1].

1: Human ISPD Is a Cytidyltransferase Required for Dystroglycan O-Mannosylation. Riemersma M, Froese DS, van Tol W, Engelke UF, Kopec J, van Scherpenzeel M, Ashikov A, Krojer T, von Delft F, Tessari M, Buczkowska A, Swiezewska E, Jae LT, Brummelkamp TR, Manya H, Endo T, van Bokhoven H, Yue WW, Lefeber DJ; Chem Biol. 2015;22:1643-1652. PMID:26687144