N-acetyl glucosamine (GlcNAc) transferase that catalyzes the transfer of GlcNAc via a beta1->3 linkage from UDP-GlcNAc to the non-reducing terminal galactose (Gal) in the linearly growing chain of N- and O-linked keratan sulfate proteoglycans. Cooperates with B4GALT4 galactosyltransferase and CHST6 and CHST1 sulfotransferases to construct and elongate mono- and disulfated disaccharide units [->3Galbeta1->4(6-sulfoGlcNAcbeta)1->] and [->3(6-sulfoGalbeta)1->4(6-sulfoGlcNAcbeta)1->] within keratan sulfate polymer (By similarity). Involved in biosynthesis of N-linked keratan sulfate proteoglycans in cornea, with an impact on proteoglycan fibril organization and corneal transparency (PubMed:29625490). May play a role in the maintenance of tissue architecture by suppressing cellular motility and invasion (PubMed:12061784). Protein modification; protein glycosylation. Strongly expressed in placenta and colon. Moderately expressed in lung, stomach, small intestine and kidney. Very weakly expressed in cerebrum, cerebellum, heart and testis. Mutant mice are born at the expected Mendelian rate and have normal developmental and reproductive potential. They develop an abnormal corneal ultrastructure characterized by a lack of keratan sulfate proteoglycans that appears to be compensated by increased amount of elongated, branched electron dense chondroitin sulfate/dermatan sulfate proteoglycan filaments. Belongs to the glycosyltransferase 31 family.