Shiokawa K, Fu Y C, Kawazoe Y, Yamana K
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan.
Development. 1987 Jul;100(3):513-23. doi: 10.1242/dev.100.3.513.
Recently, we found that rRNA synthesis in dissociated embryonic cells of Xenopus laevis is selectively inhibited by ammonium salts added to their surrounding medium. Similar effects were also observed in cells treated with amines. In this report, we analysed in more detail the effects of an ammonium salt and trimethylamine on rRNA synthesis in Xenopus embryonic cells cultured under several different conditions. Results obtained showed that ammonia and trimethylamine inhibit formation of 40S pre-rRNA, without inducing breakdown (wastage) or aberrant processing of the 40S pre-rRNA. Such inhibitory effects were also shown not to be due to interference with cellular ATP level. Furthermore, we found that the effects of both ammonium salt and trimethylamine were completely abolished when Na+ in the culture medium of the testing cells was replaced by choline ions. These results favour the view that the inhibition of rRNA synthesis by ammonia and amine is realized at the transcriptional level or at the step before the formation of 40S pre-rRNA, most probably via a slight increase of intracellular pH, but not via an inhibition in energy-generating systems.
最近，我们发现，添加到非洲爪蟾解离胚胎细胞周围培养基中的铵盐可选择性抑制其rRNA合成。在用胺处理的细胞中也观察到了类似的效应。在本报告中，我们更详细地分析了铵盐和三甲胺对在几种不同条件下培养的非洲爪蟾胚胎细胞中rRNA合成的影响。所得结果表明，氨和三甲胺抑制40S前体rRNA的形成，而不会诱导40S前体rRNA的降解（损耗）或异常加工。这种抑制作用也并非由于干扰细胞ATP水平所致。此外，我们发现，当测试细胞培养基中的Na+被胆碱离子取代时，铵盐和三甲胺的作用均完全消除。这些结果支持这样一种观点，即氨和胺对rRNA合成的抑制作用是在转录水平或在40S前体rRNA形成之前的步骤实现的，很可能是通过细胞内pH值的轻微升高，而不是通过抑制能量产生系统。
