Biogenesis of cell division sites in ftsA and ftsZ filaments.

The development of nascent cell division sites was studied in Escherichia coli strains containing ftsAts and ftsZts mutations in which septal development is arrested after shift to the restrictive temperature. Division sites were studied by measuring positions of plasmolysis bays, a visible marker for periseptal annuli. Annuli are circumferential zones of membrane adhesion which represent the earliest known structural differentiation at developing septal sites. Two patterns of annulus development were observed in the mutant strains. Normal numbers of new annuli were generated in filaments of both mutants, but in ftsZ filaments annuli failed to mature and to become properly localized, suggesting that ftsZ gene product is first required for maturation of annuli. In contrast, mature annuli accumulated at division sites in ftsA filaments, suggesting that the ftsA gene product is required at a stage after maturation and localization of nascent annuli.