Mnt2p and Mnt3p of Saccharomyces cerevisiae are members of the Mnn1p family of alpha-1,3-mannosyltransferases responsible for adding the terminal mannose residues of O-linked oligosaccharides

The genome of Saccharomyces cerevisiae contains five genes that encode type II transmembrane proteins with significant amino acid similarity to the al pha-1,3-mannosyltransferase Mnn1p, The roles of the three genes most closel y related to MNN1 were examined in mutants carrying single and multiple com binations of the disrupted genes. Paper chromatographic analysis of [2-H-3] mannose-labeled O-linked oligosaccharides released by beta-elimination show ed that the MNT2 (YGL257c) and MNT3 (YIL014w) genes in combination with MNN 1 have overlapping roles in the addition of the fourth and fifth alpha-1,3- linked mannose residues to form Man(4) and Mans oligosaccharides whereas MN T4 (YNR059w) does not appear to be required for O-glycan synthesis.