Isolation of the ALG5 Locus Encoding the UDP‐Glucose:Dolichyl‐Phosphate Glucosyltransferase from Saccharomyces cerevisiae

Abstract

UDP‐glucose:dolichyl‐phosphate glucosyltransferase is a transmembrane‐bound enzyme of the endoplasmic reticulum involved in protein N‐linked glycosylation. This enzyme catalyzes the transfer of glucose from UDP‐glucose to dolichyl phosphate. The structural gene encoding this transferase from Saccharomyces cerevisiae was isolated by complementation of an alg5‐1 mutation. DNA sequencing of ALG5 revealed an open‐reading frame of 1002 bases encoding a transmembrane protein of molecular mass 38.3 kDa. Overexpression of Alg5p in both yeast and Escherichia coli results in an increase of UDP‐glucose: dolichyl‐phosphate glucosyltransferase activity, whereas a deletion of the yeast gene leads to a loss of this activity and a concomitant underglycosylation of carboxypeptidase Y. The ALG5 protein has sequence similarity to the GDP‐mannose: dolichyl‐phosphate mannosyltransferase (Dpm1p) from S. cerevisiae. Topological studies indicate that UDP‐glucose:dolichyl‐phosphate glucosyltransferase is a transmembrane protein that spans the membrane several times. Copyright © 1994, Wiley Blackwell. All rights reserved