Hydroxylation of Saccharomyces Cerevisiae Ceramides Requires Sur2p and Scs7p

The Saccharomyces cerevisiae SCS7 and SUR2 genes are members of a gene family that encodes enzymes that desaturate or hydroxylate lipids. Sur2p is required for the hydroxylation of C-4 of the sphingoid moiety of ceramide, and Scs7p is required for the hydroxylation of the very long chain fatty acid. Neither SCS7 nor SUR2 are essential for growth, and lack of the Scs7p- or Sur2p-dependent hydroxylation does not prevent the synthesis of mannosyldiinositolphosphorylceramide, the mature sphingolipid found in yeast. Deletion of either gene suppresses the Ca2+-sensitive phenotype of csg2Delta mutants, which arises from overaccumulation of inositolphosphorylceramide due to a defect in sphingolipid mannosylation. Characterization of scs7 and sur2 mutants is expected to provide insight into the function of ceramide hydroxylation.