Peptidoglycan polymerase that is essential for cell division (Probable). Functions probably in conjunction with the penicillin-binding protein 3 (ftsI) (PubMed:9603865, PubMed:11807049). Required for localization of FtsI (PubMed:11807049). [GlcNAc-(1->4)-Mur2Ac(oyl-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala)](n)-di-trans,octa-cis-undecaprenyl diphosphate + beta-D-GlcNAc-(1->4)-Mur2Ac(oyl-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala)-di-trans,octa-cis-undecaprenyl diphosphate = [GlcNAc-(1->4)-Mur2Ac(oyl-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala)](n+1)-di-trans-octa-cis-undecaprenyl diphosphate + di-trans,octa-cis-undecaprenyl diphosphate + H(+) Cell wall biogenesis; peptidoglycan biosynthesis. Forms a complex with FtsI. Interacts also with FtsL, FtsQ and FtsN. Localizes to the division septum. Localization requires FtsZ, FtsA, FtsQ and FtsL, but not FtsI. The periplasmic loop between transmembrane domains 7 and 8 is essential for activity and the loop between transmembrane domains 9 and 10 is involved in the recruitment of FtsI at the division site. Belongs to the SEDS family. FtsW subfamily. Has previously been proposed to be a lipid II flippase that transports lipid-linked peptidoglycan precursors from the inner to the outer leaflet of the cytoplasmic membrane (PubMed:21386816, PubMed:24711460), but recent evidence suggests that FtsW may function as a peptidoglycan polymerase (PubMed:27643381). The identity of the lipid II flippase is still controversial with conflicting in vivo and in vitro results, but MurJ (AC P0AF16) is probably the lipid II flippase.