SYNTHESIS OF MONOHYDROXYLATED INOSITOLPHOSPHORYLCERAMIDE (IPC-C) IN SACCHAROMYCES-CEREVISIAE REQUIRES SCS7P, A PROTEIN WITH BOTH A CYTOCHROME B(5)-LIKE DOMAIN AND A HYDROXYLASE DESATURASE DOMAIN/

Saccharomyces cerevisiae mutants lacking Scs7p fail to accumulate the inositolphosphorylceramide (IPC) species, IPC-C, which is the predomin ant form found in wild-type cells. Instead scs7 mutants accumulate an IPC-B species believed to be unhydroxylated on the amide-linked C-26-f atty acid. Elimination of the SCS7 gene suppresses the Ca2+-sensitive phenotype of csg1 and csg2 mutants. The CSG1 and CSG2 genes are requir ed for mannosylation of IPC-C and accumulation of IPC-C by the csg mut ants renders them Ca2+-sensitive. The SCS7 gene encodes a protein that contains both a cytochrome b(5)-like domain and a domain that resembl es the family of cytochrome b(5)-dependent enzymes that use iron and o xygen to catalyse desaturation or hydroxylation of fatty acids and ste rols. Scs7p is therefore likely to be the enzyme that hydroxylates the C-26-fatty acid of IPC-C. (C) 1998 John Wiley & Sons, Ltd.