Catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, the transfer of an N-acetyl-D-galactosamine residue to a serine or threonine residue on the protein receptor. Has activity toward Muc5Ac and EA2 peptide substrates.
Subcellular locations: Golgi apparatus membrane
Widely expressed. Expressed at high level in small intestine, and at intermediate levels in stomach, pancreas, ovary, thyroid gland and spleen. Weakly expressed in other tissues.