This gene encodes GalNAc transferase 7, a member of the GalNAc-transferase family. The enzyme encoded by this gene controls the initiation step of mucin-type O-linked protein glycosylation and transfer of N-acetylgalactosamine to serine and threonine amino acid residues. This enzyme is a type II transmembrane protein and shares common sequence motifs with other family members. Unlike other family members, this enzyme shows exclusive specificity for partially GalNAc-glycosylated acceptor substrates and shows no activity with non-glycosylated peptides. This protein may function as a follow-up enzyme in the initiation step of O-glycosylation.