label: acetylgalactosaminyl-O-glycosyl-glycoprotein beta-1,3-N-acetylglucosaminyltransferase activity
label_lc: acetylgalactosaminyl-o-glycosyl-glycoprotein beta-1,3-n-acetylglucosaminyltransferase activity
description: "Catalysis of the reaction: 3-O-N-acetyl-D-galactosalaminyl-[protein] + UDP-N-acetyl-D-glucosamine = 3-O-N-acetyl-beta-D-glucosaminyl-1,3-N-acetyl-D-galactosaminyl-[protein] + UDP. Linkage of the glycan to the protein occurs via the oxygen atom in the side chain of an L-serine or L-threonine residue."