| Abstract: | Synchronous cell division in an arginine auxotroph and a histidine auxotroph of Escherichia coli was obtained after starving for the required amino acid for 1 hr. However, cell division was not synchronized after starvation for 1 hr in another arginine auxotroph. This difference is proposed to depend on differences in the concentrations of polyamines in the cells. During amino acid starvation the ratio of putrescine concentration to spermidine concentration decreased in all strains, but it recovered afterward more rapidly in the third strain than in the other two. The cells divided when the ratio returned to normal in the Arg(-) mutants. Added putrescine permitted some of the cells of the first two mutants to divide sooner after amino acid starvation and thus eliminated synchrony. Spermidine added alone had no effect, but, when it was added together with putrescine, it restored synchronous division. Synchrony was established in the third mutant by adding spermidine after arginine starvation. Thus, both the variations in polyamine content and the effects of added polyamines suggest that the polyamines are essential in permitting cell division. We suggest that the molar ratio of putrescine to spermidine can be a critical factor for cell division. This effect of polyamines seems to be specific for cell division. Amino acid starvation does not induce delays in subsequent mass increase or deoxyribonucleic acid synthesis. Possible mechanisms of polyamine action are discussed. |
