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 (, ). May participate in synthesis of oncofetal fibronectin . Has activity toward MUC1A, MUC2, EA2 and fibronectin peptides . Glycosylates FGF23 .
Subcellular locations: Golgi apparatus membrane
Expressed in placenta and trachea. Weakly expressed in brain and pancreas. Expressed in fibroblast. Weakly or not expressed in lung, liver, muscle, kidney, spleen, thymus, prostate, testis, ovary, intestine, colon, leukocyte, stomach, thyroid, spinal cord, lymph node, trachea, adrenal gland and bone marrow.