Involved in the biosynthesis of the disaccharide D-N-acetylglucosamine-L-rhamnose which plays an important role in the mycobacterial cell wall as a linker connecting arabinogalactan and peptidoglycan via a phosphodiester linkage. Catalyzes the transfer of the N-acetylglucosamine-1-phosphate (GlcNAc-1P) moiety from UDP-GlcNAc onto the carrier lipid decaprenyl phosphate (C50-P), yielding GlcNAc-pyrophosphoryl-decaprenyl (GlcNAc-PP-C50). trans,octa-cis-decaprenyl phosphate + UDP-N-acetyl-alpha-D-glucosamine = N-acetyl-alpha-D-glucosaminyl-1-diphospho-trans,octa-cis-decaprenol + UMP Cell wall biogenesis; cell wall polysaccharide biosynthesis. Mycobacteria use decaprenyl phosphate (C50-P) as a lipid carrier in all known cell wall biosynthetic pathways, rather than the usual undecaprenyl phosphate (C55-P) usually used in Gram-negative bacteria. Belongs to the glycosyltransferase 4 family. WecA subfamily.