Dolichol phosphate mannose synthase from the filamentous fungus Trichoderma reesei belongs to the human and Schizosaccharomyces pombe class of the enzyme

Dolichol phosphate mannose (DPM) synthase activity, which is required in N- glycosylation, O-mannosylation, and glycosylphosphatidylinositol membrane a nchoring of protein, has been postulated to regulate the Trichoderma reesei secretory pathway. We have cloned a T.reesei cDNA that encodes a 243 amino acid protein whose amino acid sequence shows 67% and 65% identity, respect ively, to the Schizosaccharomyces pombe and human DPM synthases, and which lacks the COOH-terminal hydrophobic domain characteristic of the Saccharomy ces cerevisiae class of synthase, The Trichoderma dpm1 (Trdpm1) gene comple ments a lethal null mutation in the S.pombe dpm1(+) gene, but neither resto res viability of a S.cerevisiae dpm1-disruptant nor complements the tempera ture-sensitivity of the S.cerevisiae dpm1-6 mutant. The T.reesei DPM syntha se is therefore a member of the "human" class of enzyme. Overexpression of Trdpm1 in a dpm1(+)::his7/dpm1(+) S.pombe diploid resulted in a 4-fold incr ease in specific DPM synthase activity. However, neither the wild type T.re esei DPM synthase, nor a chimera consisting of this protein and the hydroph obic COOH terminus of the S.cerevisiae DPM synthase, complemented an S.cere visiae dpm1 null mutant or gave active enzyme when expressed in E.coli, The level of the Tpdpm1 mRNA in T.reesei QM9414 strain was dependent on the co mposition of the culture medium. Expression levels of Trdpm1 were directly correlated with the protein secretory capacity of the fungus.