Title: Accumulation of a Protein Required for Division During the Cell Cycle of <i>Escherichia coli</i>
Abstract: A heat-labile protein required for division accumulates during the duplication cycle of Escherichia coli . Its formation appears to commence shortly after the cell divides, and it reaches a maximal amount shortly before the next division. A plausible mechanism for timing cell division depends on building up the critical amount of this protein. Completion of deoxyribonucleic acid (DNA) replication is also necessary for division to occur, but it does not uniquely initiate division. The evidence for these conclusions comes from heat-shock experiments; heating to 45 C for 15 min delays division increasingly with the age of a cell. A heat shock given near the end of a cycle delays division for about 30 min, whereas at the beginning of the cycle it hardly affects division. The net result is synchronization of cell division. The effect of heat is increased in bacteria which have incorporated p -fluoro-phenylalanine into their proteins. When the incorporation is early and the heat shock is late in the cycle, division is delayed by about 30 min, indicating that the division protein is synthesized early even though its sensitivity is not observed until later. At any time in the cell cycle, heat shock simply delays total protein and DNA synthesis ( 3 H-thymidine uptake) for approximately 14 min. DNA replication and cell division are thus discoordinated, since DNA replication is not synchronized by the treatment.