Intrinsic instability of the essential cell division protein FtsL of Bacillus subtilis and a role for DivIB protein in FtsL turnover

Cell division in most eubacteria is driven by an assembly of about eight co nserved division proteins. These proteins form a ring structure that constr icts in parallel with the formation of the division septum. Here, we show t hat one of the division proteins, FtsL, is highly unstable. We also show th at the protein is targeted to the ring structure and that targeting occurs in concert with the recruitment of several other membrane-associated divisi on proteins. FtsL stability is further reduced in the absence of DivIB prot ein (probably homologous to E. coli FtsQ) at high temperature, suggesting t hat DivIB is involved in the control of FtsL turnover. The reduced stabilit y of FtsL may explain the temperature dependence of divIB mutants, because their phenotype can be suppressed by overexpression of FtsL. The results pr ovide new insights into the roles of the FtsL and DivIB proteins in bacteri al cell division.