Synthesis of monohydroxylated inositolphosphorylceramide (IPC-C) inSaccharomyces cerevisiae requires Scs7p, a protein with both a cytochrome b5-like domain and a hydroxylase/desaturase domain

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Abstract
Saccharomyces cerevisiae mutants lacking Scs7p fail to accumulate the inositolphosphorylceramide (IPC) species, IPC‐C, which is the predominant form found in wild‐type cells. Instead scs7 mutants accumulate an IPC‐B species believed to be unhydroxylated on the amide‐linked C26‐fatty acid. Elimination of the SCS7 gene suppresses the Ca2+‐sensitive phenotype of csg1 and csg2 mutants. The CSG1 and CSG2 genes are required for mannosylation of IPC‐C and accumulation of IPC‐C by the csg mutants renders them Ca2+‐sensitive. The SCS7 gene encodes a protein that contains both a cytochrome b5‐like domain and a domain that resembles the family of cytochrome b5‐dependent enzymes that use iron and oxygen to catalyse desaturation or hydroxylation of fatty acids and sterols. Scs7p is therefore likely to be the enzyme that hydroxylates the C26‐fatty acid of IPC‐C. © 1998 John Wiley & Sons, Ltd.