Abstract
Cell division in Escherichia coli begins by assembling three proteins, FtsZ, FtsA, and ZipA, to form a proto-ring at midcell. These proteins nucleate an assembly of at least 35 components, the divisome. The structuring of FtsZ to form a ring and the processes that effect constriction have been explained by alternative but not mutually exclusive mechanisms. We discuss how FtsA and ZipA provide anchoring of the cytoplasmic FtsZ to the membrane and how a temporal sequence of alternative protein interactions may operate in the maturation and stability of the proto-ring. How the force needed for constriction is generated and how the proto-ring proteins relate to peptidoglycan synthesis remain as the main challenges for future research.