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. 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 also with FtsI and FtsN. Localizes to the division septum. Localization requires FtsQ and FtsL, but not FtsW and FtsI. Localization of FtsB and FtsL is codependent. The transmembrane segment and the membrane-proximal periplasmic region, which forms a coiled-coil structure, are required for interaction with FtsL and recruitment of downstream division proteins. The C-terminal region is required for interaction with FtsQ, but is not required for recruitment of the downstream division protein FtsI. Contains a leucine zipper-like (LZ) motif, which is required for optimal interaction with FtsL. Mutants form long filaments, but DNA segregation is not affected. The C-terminal domain of FtsB is degraded in the absence of either FtsL or FtsQ. Belongs to the FtsB family.