Reaction catalyzed by N-acetylgalactosamine-N,N'-diacetylbacillosaminyl-diphospho-undecaprenol 4-alpha-N-acetylgalactosaminyltransferase (2.4.1.291)

		+			=			+
	UDP-N-acetyl-alpha-D-galactosamine	+		N-acetyl-D-galactosaminyl-alpha-(1->3)-N,N'-diacetyl-alpha-D-bacillosaminyl-diphospho-tritrans,heptacis-undecaprenol	=		UDP	+		N-acetyl-D-galactosaminyl-alpha-(1->4)-N-acetyl-D-galactosaminyl-alpha-(1->3)-N,N'-diacetyl-alpha-D-bacillosaminyl-diphospho-tritrans,heptacis-undecaprenol