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, Su r2p is required for the hydroxylation of C-4 of the sphingoid moiety o f ceramide, and Scs7p is required for the hydroxylation of the very lo ng chain fatty acid, Neither SCS7 nor SUR2 are essential for growth, a nd lack of the Scs7p- or Sur2p-dependent hydroxylation does not preven t the synthesis of mannosyldiinositolphosphorylceramide, the mature sp hingolipid found in yeast, Deletion of either gene suppresses the Ca2-sensitive phenotype of csg2 Delta mutants, which arises from overaccu mulation 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.