Hoober J K, Marks D B, Keller B J, Margulies M M
J Cell Biol. 1982 Nov;95(2 Pt 1):552-8. doi: 10.1083/jcb.95.2.552.
The amount of messenger RNA (mRNA) for polypeptides of the chlorophyll a/b-protein complex of thylakoid membranes in etiolated and greening cells of Chlamydomonas reinhardtii y-1 was examined by immunoprecipitation and electrophoresis of products of in vitro translation to determine at which stage production of these polypeptides is regulated. Cells grown 4 d in the dark at 25 degrees C contained small amounts of translatable mRNA for the major membrane polypeptides. Exposure of these etiolated cells to light, under conditions in which the membrane polypeptides accumulated, resulted in a significant increase in the quantity of the mRNA. In contrast, when etiolated cells were incubated for 1-2 h in the dark at 38 degrees C, translation assays indicated that mRNA for the membrane polypeptides became abundant. Moreover, the quantity of the mRNA did not increase when these cells subsequently were exposed to light. Therefore, at 38 degrees C the cellular level of the polypeptides is not regulated by synthesis of mRNA. The in vitro synthesized polypeptides, which were precipitated with antibodies prepared against the purified thylakoid polypeptides, had apparent molecular weights of 31,500 and 30,000. The corresponding immunoprecipitated polypeptides made in vivo had apparent molecular weights of 29,500 and 26,000. Thus, the membrane polypeptides are made as precursors. No net accumulation of the polypeptides occurred in cells in the dark at 38 degrees C, but immunoreactive polypeptides the size of the mature membrane components were labeled during incubation of cells with [14C]acetate in the dark. These results indicated that the mRNA was translated in the dark, but since the polypeptides did not accumulate, the products of translation were probably degraded. We conclude from our experiments that at 25 degrees C production of the polypeptides is regulated by the level of translatable mRNA in the cells. At 38 degrees C, however, the accumulation of the polypeptides is controlled by posttranslational processes.
通过对莱茵衣藻y-1黄化和绿化细胞中类囊体膜叶绿素a/b蛋白复合体多肽的信使核糖核酸（mRNA）进行免疫沉淀和体外翻译产物电泳，研究了这些多肽在哪个阶段的产生受到调控。在25℃黑暗中生长4天的细胞含有少量主要膜多肽的可翻译mRNA。将这些黄化细胞置于膜多肽积累的光照条件下，mRNA的量显著增加。相反，当黄化细胞在38℃黑暗中孵育1-2小时时，翻译分析表明膜多肽的mRNA变得丰富。此外，当这些细胞随后暴露于光照下时，mRNA的量没有增加。因此，在38℃时，多肽的细胞水平不受mRNA合成的调控。用针对纯化的类囊体多肽制备的抗体沉淀的体外合成多肽具有明显的分子量，分别为31,500和30,000。体内相应的免疫沉淀多肽具有明显的分子量，分别为29,500和26,000。因此，膜多肽是以前体形式合成的。在38℃黑暗中的细胞中多肽没有净积累，但在黑暗中用[14C]乙酸孵育细胞期间，标记了成熟膜成分大小的免疫反应性多肽。这些结果表明mRNA在黑暗中被翻译，但由于多肽没有积累，翻译产物可能被降解。我们从实验中得出结论，在25℃时，多肽的产生受细胞中可翻译mRNA水平的调控。然而，在38℃时，多肽的积累受翻译后过程的控制。
