Catalysis of the reaction: UDP-N-acetyl-D-glucosamine + (N-acetyl-beta-D-glucosaminyl-1,2)-alpha-D-mannosyl-1,3-(beta-N-acetyl-D-glucosaminyl-1,2-alpha-D-mannosyl-1,6)-beta-D-mannosyl-R = UDP + N-acetyl-beta-D-glucosaminyl-1,4-(N-acetyl-D-glucosaminyl-1,2)-alpha-D-mannosyl-1,3-(beta-N-acetyl-D-glucosaminyl-1,2-alpha-D-mannosyl-1,6)-beta-D-mannosyl-R.
N-acetylglucosaminyltransferase IV activity