polypeptide N-acetylgalactosaminyltransferase activity https://github.com/geneontology/go-ontology/issues/30193 Catalysis of the reaction: UDP-N-acetyl-D-galactosamine + polypeptide = UDP + N-acetyl-D-galactosaminyl-polypeptide. This reaction is the modification of serine or threonine residues in polypeptide chains by the transfer of a N-acetylgalactose from UDP-N-acetylgalactose to the hydroxyl group of the amino acid; it is the first step in O-glycan biosynthesis. glycoprotein acetylgalactosaminyltransferase activity UDP-N-acetylgalactosamine-protein N-acetylgalactosaminyltransferase activity molecular_function UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase activity polypeptide-N-acetylgalactosamine transferase activity Reactome:R-HSA-8851619 UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyl-transferase activity Reactome:R-HSA-9683760 Reactome:R-HSA-5096537 protein-UDP acetylgalactosaminyltransferase activity MetaCyc:2.4.1.41-RXN Reactome:R-HSA-5096532 UDP-N-acetylgalactosamine:kappa-casein polypeptide N-acetylgalactosaminyltransferase activity UDP-acetylgalactosamine:peptide-N-galactosaminyltransferase activity UDP-N-acetylgalactosamine-glycoprotein N-acetylgalactosaminyltransferase activity UDP-acetylgalactosamine-glycoprotein acetylgalactosaminyltransferase activity Reactome:R-HSA-9694438 EC:2.4.1.41 UDP-GalNAc:polypeptide N-acetylgalactosaminyl transferase activity UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase activity UDP-N-acetylgalactosamine:protein N-acetylgalactosaminyl transferase activity UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferase activity GO:0004653 uridine diphosphoacetylgalactosamine-glycoprotein acetylgalactosaminyltransferase activity Reactome:R-HSA-913675 acetylgalactosaminyltransferase activity catalytic activity, acting on a protein