Campbell J M, Weissbach H
J Biol Chem. 1980 May 25;255(10):4691-7.
The uptake of nucleosides and the synthesis of RNA in Tetrahymena thermophila were examined following amino acid starvation. Omission of leucine, phenylalanine, or arginine from the medium resulted in a rapid decrease in the incorporation of [3H]uridine into the acid-soluble pool and acid-insoluble material (RNA). Amino acid starvation inhibited the uptake of all ribo- and deoxyribonucleosides tested but did not affect the uptake of amino acids or glucose. In addition, under the conditions used, the omission of an amino acid did not result in a large decrease in amino acid incorporation into total protein. Treatment of cells with cycloheximide or emetine gave results similar to the effects of amino acid starvation, but in these experiments the inhibition of protein synthesis was essentially complete. Nucleotide pool sizes were also measured following amino acid starvation. ATP and UTP levels were essentially unchanged, but the dTTP pool size was decreased by 40%. The decrease in RNA synthesis in vivo in the absence of an essential amino acid was reflected in the endogenous RNA synthetic activity of isolated nuclei. However, when solubilized RNA polymerase activity was measured with calf thymus DNA as template, no significant difference was observed between control and amino acid-starved cells.
在嗜热四膜虫中，研究了氨基酸饥饿后核苷的摄取和RNA的合成。培养基中缺少亮氨酸、苯丙氨酸或精氨酸会导致[3H]尿苷掺入酸溶性池和酸不溶性物质（RNA）的量迅速减少。氨基酸饥饿抑制了所有测试的核糖核苷和脱氧核糖核苷的摄取，但不影响氨基酸或葡萄糖的摄取。此外，在所使用的条件下，缺少一种氨基酸不会导致氨基酸掺入总蛋白的量大幅减少。用环己酰亚胺或吐根碱处理细胞得到的结果与氨基酸饥饿的影响相似，但在这些实验中，蛋白质合成的抑制基本完全。还测定了氨基酸饥饿后的核苷酸池大小。ATP和UTP水平基本不变，但dTTP池大小减少了40%。在缺乏必需氨基酸的情况下，体内RNA合成的减少反映在分离细胞核的内源性RNA合成活性上。然而，当以小牛胸腺DNA为模板测量可溶性RNA聚合酶活性时，对照细胞和氨基酸饥饿细胞之间未观察到显著差异。
