Horisberger M, Amos H
Biochem J. 1970 Apr;117(2):347-53. doi: 10.1042/bj1170347.
The failure to induce glutamine synthetase in retinal cells with hydrocortisone at 27 degrees C (37 degrees C is the normal temperature for induction) led to a study of some aspects of RNA synthesis at 27 degrees C by using the method of selective labelling with radioactive precursors, sucrose-density-gradient centrifugation and radioautography. The low-temperature treatment not only decreases the rate of RNA synthesis but also interferes with the general pattern of RNA maturation and distribution. It has been found that nuclear-cytoplasmic exchange is severely altered at low temperature and may be an explanation of the failure to induce the enzyme. When the temperature is raised from 27 degrees C to 37 degrees C, the incorporation of exogenous radioactive uridine into the RNA is distorted by a pool-dilution effect that results in an ;over-shoot' phenomenon. The kinetics of labelled uridine equilibration into the UMP pool accounts for the difficulty encountered by many investigators in ;chase' efforts with unlabelled nucleosides.
在27摄氏度（37摄氏度是诱导的正常温度）下用氢化可的松未能在视网膜细胞中诱导谷氨酰胺合成酶，这导致了通过使用放射性前体的选择性标记、蔗糖密度梯度离心和放射自显影方法对27摄氏度下RNA合成的某些方面进行研究。低温处理不仅降低了RNA合成的速率，还干扰了RNA成熟和分布的总体模式。已经发现，低温下核质交换会严重改变，这可能是未能诱导该酶的一个解释。当温度从27摄氏度升高到37摄氏度时，外源放射性尿苷掺入RNA会因池稀释效应而扭曲，从而导致“过冲”现象。标记的尿苷平衡进入UMP池的动力学解释了许多研究人员在使用未标记核苷进行“追踪”时遇到的困难。
