A defective recA gene, which is involved in recombination, is shown in this article to permit limited cell division, when deoxyribonucleic acid (DNA) synthesis is blocked. Thymidine starvation or nalidixic acid blocked DNA synthesis, and stopped cell division of a rec+thy− strain of Escherichia coli. However, with the same treatments, a recAthy− strain could continue to divide for at least 5 hr, and cell numbers increased 2.5- to 4-fold. After several hours of thymidine starvation, the culture contained very long cells (snakes) and small (normal-sized) cells. The short cells contained very little, if any, DNA. Cells of all ages divided in the absence of thymidine. Specific differences in membrane proteins were observed between thymidine-starved rec+ and recA cells, as expected from previous experiments in which these proteins were associated with cell division and DNA synthesis. It is proposed that septum formation is controlled negatively by the recA+ gene
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