Responsible for the synthesis of complex-type N-linked oligosaccharides in many glycoproteins as well as the carbohydrate moieties of glycolipids. Can produce lactose (By similarity). D-glucose + UDP-alpha-D-galactose = H(+) + lactose + UDP an N-acetyl-beta-D-glucosaminyl derivative + UDP-alpha-D-galactose = a beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + H(+) + UDP N-acetyl-D-glucosamine + UDP-alpha-D-galactose = beta-D-galactosyl-(1->4)-N-acetyl-D-glucosamine + H(+) + UDP Protein modification; protein glycosylation. Trans cisternae of Golgi stack. Belongs to the glycosyltransferase 7 family.