EOG88974P	GO:0004653	1/4	polypeptide N-acetylgalactosaminyltransferase activity	molecular_function	"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." [EC:2.4.1.41, ISBN:0879695595]