Autorepressor Model for Control of DNA Replication

THE rate of cell division in Escherichia coli seems to be determined by the frequency of initiation of chromosome replication1,2. It is often assumed that replication begins when a certain amount of an intracellular protein(s) (the initiator(s)) has accumulated or, alternatively, when the concentration of an inhibitor of the initiator is reduced below a threshold level by an increase in cell volume1-5. All these models presuppose that initiator is made at all growth rates as a constant fraction of total protein4-6 or in proportion to cell mass or volume2,7. So far, no mechanism for this has been suggested and we propose that a simple feedback control system, the elements of which exist in bacteria, might answer this problem.