The protein encoded by this gene is a beta-1,3-N-acetylglucosaminyltransferase that adds an N-acetylglucosamine moiety to N-acetylgalactosamine-modified serine or threonine. The encoded enzyme is responsible for creating the core 3 structure of O-glycans, which are important components of mucin-type glycoproteins. [provided by RefSeq, Dec 2016].