Fig 4. Failsafe mechanisms couple division and DNA replication in the bacterial cell cycle.

DNA replication (blue) and growth (beige) are ongoing and the division ring is present for approximately the second half of each cell cycle. A division-dependent failsafe mechanism ensures one DNA replication initiation occurs per each division. Failure to divide leads to a block in replication initiation followed by entry into a terminal cell cycle arrest at the PONR, equivalent to a eukaryotic G₀ state. A second initiation-dependent failsafe mechanism ensures that cells impaired in the initiation of DNA replication do not assemble division rings. The dashed arrows indicate hypothetical localizations of the failsafe mechanisms.