Cell wall formation (PubMed:1649817). Catalyzes the transfer of a GlcNAc subunit on undecaprenyl-pyrophosphoryl-MurNAc-pentapeptide (lipid intermediate I) to form undecaprenyl-pyrophosphoryl-MurNAc-(pentapeptide)GlcNAc (lipid intermediate II) (PubMed:1649817, PubMed:12538870). Strongly prefers UDP to CDP, GDP, ADP and TDP (PubMed:12538870). di-trans-octa-cis-undecaprenyl diphospho-N-acetyl-alpha-D-muramoyl-L-alanyl-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine + UDP-N-acetyl-alpha-D-glucosamine = di-trans-octa-cis-undecaprenyl diphospho-[N-acetyl-alpha-D-glucosaminyl-(1->4)]-N-acetyl-alpha-D-muramoyl-L-alanyl-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine + H(+) + UDP kcat is 837 min(-1). Cell wall biogenesis; peptidoglycan biosynthesis. Homodimer (PubMed:12538870). Associates with MreB and MraY (PubMed:17640276). Randomly distributed in the cell envelope with a higher intensity at the division site. Mid-cell localization requires divisome components. Inactivation of the gene rapidly inhibits peptidoglycan synthesis in exponentially growing cells. Belongs to the glycosyltransferase 28 family. MurG subfamily.