Mucin type O-glycosylation is a widespread modification of eukaryotic pro-teins. The transfer of N-acetylgalactosamine to selected serine or threonine residues is catalyzed by a family of polypeptide N-acetylgalactosaminyl-transferases localized in the Golgi apparatus. The most abundant elonga-tion of O-glycans is the addition of a b1-3 linked galactose by the core-1 b1-3 galactosyltransferase (core-1b3GalT), thereby building the T-antigen or core-1 structure Gal(b1-3)GalNAc(a1-O).
