This family includes eukaryotic UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) and archaeal GPT-like glycosyltransferases. Eukaryotic GPT catalyzes the transfer of GlcNAc-1-P from UDP-GlcNAc to dolichol-P to form GlcNAc-P-P-dolichol. The reaction is the first step in the assembly of dolichol-linked oligosaccharide intermediates and is essential for eukaryotic N-linked glycosylation. GPT activity has been identified in all eukaryotic cells examined to date. Evidence for the existence of the N-glycosylation pathway in archaea has emerged and genes responsible for the pathway have been identified. A glycosyl transferase gene Mv1751 in M. voltae encodes for the enzyme that carries out the first step in the pathway, the attachment of GlcNAc to a dolichol lipid carrier in the membrane. A lethal mutation in the alg7 (GPT) gene in Saccharomyces cerevisiae was successfully complemented with Mv1751, the archaeal gene, indicating eukaryotic and archaeal enzymes may use the same substrates and are evolutionarily closer than the bacterial enzyme, which uses a different substrate.