A timing control of cell division in Escherichia coli.

The effect of heat treatment at 42degreeC on a thermosensitive division-defective strain of Escherichia coli K12, MAC1, has been studied under conditions which support a generation time of about 50 min. Synchronous cells gained simultaneously the ability to divide at 42degreeC and to divide in the presence of nalidixic acid or chloramphenicol, 20 min before physical separation of daughter cells. When synchronous cells of different ages (between 0 to 20 min after elution from an absorbent membrane) were subjected to a heat shock, division always took place 55 to 60 min after the shock. A similar treatment of an exponential culture resulted in synchronous cell division after a lag of 55 to 60 min during which no division occurred. Division is probably controlled for 40 to 45 min by the gene mutated in MAC1. Thus MAC1 cells of different ages appear to return to the same point of their division cycle when they are heated at 42degreeC. We propose that the gene mutated in MAC1 has a role in the timing control of E. coli cell division. Progress to division appears to require a fixed period in which the function controlled by the gene is performed: this period ends, under physiological conditions, when division does not require further protein or DNA synthesis.