Reaction catalyzed by N-acetyl-alpha-D-glucosaminyl-diphospho-ditrans,octacis-undecaprenol 3-alpha-mannosyltransferase (2.4.1.348)

		+			=			+
	GDP-alpha-D-mannose	+		N-acetyl-alpha-D-glucosaminyl-diphospho-ditrans,octacis-undecaprenol	=		GDP	+		alpha-D-mannosyl-(1->3)-N-acetyl-alpha-D-glucosaminyl-diphospho-ditrans,octacis-undecaprenol