Involved in peptidoglycan biosynthesis. Transports lipid-linked peptidoglycan precursors from the inner to the outer leaflet of the cytoplasmic membrane (PubMed:25918422). Not essential for growth (PubMed:19648239, PubMed:19666716). Cell wall biogenesis; peptidoglycan biosynthesis. Localizes at the septum. Expressed at low levels during vegetative growth. Expression decreases significantly during sporulation. Cells lacking this gene are viable, have no defect in growth, but produce fewer spores, slightly longer cells and show an increase in cell chain formation. Also exhibits some resistance to moenomycin (PubMed:19648239, PubMed:19666716). Mutants lacking both murJ and amj have a lethal defect in cell wall synthesis (PubMed:25918422). Belongs to the polysaccharide synthase family.