Deoxyribonucleic acid synthesis and cell division in a lon- mutant of Escherichia coli.

The lon(-) mutants of Escherichia coli form long filamentous cells after temporary inhibition of deoxyribonucleic acid (DNA) synthesis by ultraviolet irradiation, treatment with nalidixic acid, or thymine starvation. The kinetics of DNA synthesis and cell division after a period of thymine starvation have been compared in lon(+) and lon(-) cells. After this treatment, both kinds of cells recover their normal DNA to mass ratio with the same kinetics. In contrast to previous reports, cell division is found to recommence in both lon(+) and in lon(-) cells after such a temporary period of inhibition of DNA synthesis. However, the delay separating the recommencement of DNA synthesis and of cell division is approximately three times as long in lon(-) as in lon(+) cells. Low concentrations of penicillin inhibit cell division in both lon(+) and lon(-) cells. In this case, cell division recommences with the same kinetics in both strains after the removal of penicillin. This suggests that different steps in the cell division process are blocked by inhibition of DNA synthesis and by penicillin treatment. The lon(-) mutation appears to affect the former of these steps.