Essential cell division protein. May link together the upstream cell division proteins, which are predominantly cytoplasmic, with the downstream cell division proteins, which are predominantly periplasmic. May control correct divisome assembly. Part of a complex composed of FtsB, FtsL and FtsQ. The complex can be formed before its localization to the division site. This tripartite complex can be divided further into a subcomplex of FtsB and FtsL, which forms in the absence of FtsQ. Interacts with FtsA, FtsK, FtsL, FtsB, FtsW, FtsI, FtsN, FtsX and YmgF. Localizes to the division septum. Localization requires FtsZ, FtsA, ZipA and FtsK, but not FtsL, FtsI and FtsN. Insertion into the membrane requires YidC and the Sec translocase. Repressed by hydroxyurea. The C-terminal periplasmic region is necessary and sufficient for septal targeting. The transmembrane region contributes to localization to the cell division site. Three periplasmic subdomains are involved in the interactions with other cell division proteins. Localization and recruitment require two separate domains. Belongs to the FtsQ/DivIB family. FtsQ subfamily.