Hypothesis: transcriptional sensing and membrane‐domain formation initiate chromosome replication in Escherichia coli

The idea that initiation of chromosome replication occurs when cells attain a particular mass/origin ratio, the initiation mass (Donachie, 1968, Nature 219: 1077-1079; Pritchard, 1968, Heredity 23: 472-473), has been a powerful infiuence on experiments for a quarter of a century. Although the constancy of the initiation mass of populations growing with different rates has been challenged (Churchward etal.. 1981, J Bacterioi ^ 45: 12321238; Wold et al., 1994, EMBO J 13: 2097-2102), its constancy within a population at a particular growth rate has not. A mechanism for coupling the rate of initiation of replication (and so cell division) to the rate of mass increase is essential if cells are not to change progressively in size with each generation. In this communication, a mechanism for such coupling is proposed based on the concepts of genes as transcriptional sensors and the coupled transcription-translation and protein insertion into membrane (transertion).