PROTEIN O-GLYCOSYLATION IN SACCHAROMYCES-CEREVISIAE - THE PROTEIN O-MANNOSYLTRANSFERASES PMT1P AND PMT2P FUNCTION AS HETERODIMER

The protein O-maonosyltransferases Pmt1p and Pmt2p are catalyzing the O-glycosylation of serine and threonine residues in the endoplasmic re ticulum of yeast, Deletion of each of these proteins by disruption of the corresponding gene leads to a dramatic decrease of mannosyltransfe rase activity in vitro, With an anti-Pmt1p immunoaffinity column a com plex of Pmt1p and a second protein was purified; this protein turned o ut to be Pmt2p. Overexpression of Pmt1p or Pmt2p, respectively, does n ot increase mannosyltransferase activity in vitro. Overexpression of b oth mannosyltransferases together, however, raises in vitro activity t hreefold. These data indicate that Pmt1p and Pmt2p function as a compl ex catalyzing protein O-glycosylation in yeast.