preferred_name: 3-O-{beta-D-galactosyl-(1->3)-[N-acetyl-beta-D-glucosaminyl-(1->6)]-N-acetyl-alpha-D-galactosaminyl}-L-seryl-[protein] + UDP-N-acetyl-alpha-D-glucosamine = 3-O-{beta-D-GlcNAc-(1->3)-beta-D-Gal-(1->3)-[beta-D-GlcNAc-(1->6)]-alpha-D-GalNAc}-L-seryl-[protein] + UDP + H(+)