Mutations in ftsZ that confer resistance to SulA affect the interaction of FtsZ with GTP

Mutations in the essential cell division gene ftsZ confer resistance to SulA, a cell division inhibitor that is induced as part of the SOS response. In this study we have purified and characterized the gene products of six of these mutant ftsZ alleles, ftsZ1, ftsZ2, ftsZ3, ftsZ9, ftsZ100, and ftsZ114, and compared their properties to those of the wild-type gene product. The binding of GTP was differentially affected by these mutations. FtsZ3 exhibited no detectable GTP binding, and FtsZ9 and FtsZ100 exhibited markedly reduced GTP binding. In contrast, FtsZ1 and FtsZ2 bound GTP almost as well as the wild type, and FtsZ114 displayed increased GTP binding. Furthermore, we observed that all mutant FtsZ proteins exhibited markedly reduced intrinsic GTPase activity. It is likely that mutations in ftsZ that confer sulA resistance alter the conformation of the protein such that it assumes the active form.