The enzyme is involved in biosynthesis of dolichol (a long-chain polyprenol) with a saturated alpha-isoprene unit, which serves as a glycosyl carrier in protein glycosylation . The yeast Saccharomyces cerevisiae has two different enzymes that catalyse this reaction. Rer2p synthesizes a well-defined family of polyprenols of 13--18 isoprene residues with dominating C(80) (16 isoprene residues) extending to C(120), while Srt1p synthesizes mainly polyprenol with 22 isoprene subunits. Largest Srt1p products reach C(290) . The enzyme from Arabidopsis thaliana catalyses the formation of polyprenyl diphosphates with predominant carbon number C(120) .