Catalyzes the initial step of dolichol-linked oligosaccharide biosynthesis in N-linked protein glycosylation pathway: transfers GlcNAc-1-P from UDP-GlcNAc onto the carrier lipid dolichyl phosphate (P-dolichol), yielding GlcNAc-P-P-dolichol. a dolichyl phosphate + UDP-N-acetyl-alpha-D-glucosamine = N-acetyl-alpha-D-glucosaminyl-diphosphodolichol + UMP Activated by mannosylphosphoryldolichol and phospholipids such as phosphatidylglycerol and phosphatidylcholine. Inhibited by natural nucleoside antibiotic tunicamycin, which acts as a structural analog and competitor of UDP-GlcNAc. Protein modification; protein glycosylation. Homodimer. Highest activity is during the mid-phase of lactation. Partially edited. Mice die 4 to 5 days post-fertilization, just after implantation, suggesting that protein function and N-glycosylation are essential in early embryogenesis. Belongs to the glycosyltransferase 4 family.