摘要：

A study of the amino acid dependence of ribonucleoside triphosphate synthesis and its relationship to the amino acid dependence of RNA synthesis in Escherichia coli has led to the following findings: 1. (1) The conversion of UMP to UTP and CTP by plasmolyzed cells is partially amino acid-dependent in two unrelated stringent strains, but is amino acid-independent in a relaxed mutant derived from one of them. 2. (2) In whole cells of a stringent strain, the levels of UTP and CTP shrink abruptly upon exhaustion of a limiting supply of a required amino acid, at the same time as the rate of RNA synthesis is reduced. 3. (3) In whole cells of a stringent strain, the incorporation of 32PO 4 into all four ribonucleoside triphosphates is amino acid-dependent; incorporation into ATP shows the most severe amino acid-dependence. 4. (4) The amino acid-dependence of ribonucleoside triphosphate generation in stringent strains cannot be an indirect consequence of the amino acid-dependence of RNA synthesis, because RNA synthesis can be inhibited in any of three different ways without inhibiting ribonucleoside triphosphate generation. RNA synthesis was inhibited at the RNA polymerase level with actinomycin D or proflavine without inhibiting the synthesis of UTP or CTP. RNA synthesis could also be prevented by uracil starvation without significant inhibition of ATP or GTP synthesis. We suggest that the RC control system responds to amino acid deficiency by limiting ribonucleoside triphosphate synthesis, which in turn makes RNA synthesis amino acid-dependent.

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