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 a broad spectrum of substrates such as apomucin-, MUC5AC-, MUC1- and MUC2-derived peptides .
Subcellular locations: Golgi apparatus, Golgi stack membrane
Subcellular locations: Secreted
Widely expressed. Expressed in all tissues tested.