Cleveland D W, Kirschner M W, Cowan N J
Cell. 1978 Nov;15(3):1021-31. doi: 10.1016/0092-8674(78)90286-6.
The messenger RNAs coding for alpha- and beta-tubulin have been isolated from embryonic chick brain. Although the mRNAs for the two tubulin subunits have been resolved on native gels, they are very similar in molecular weight (650,000 daltons) as judged by mobility on denaturing gels containing methy mercury. The mRNAs for beta- and gamma-actin have also been resolved on native gels, but migrate as an unresolved peak (molecular weight 6500,000-700,000 daltons) under denaturing conditions. Since the nonmuscle actins are substantially smaller proteins than alpha- and beta-tubulin, the large size of chick nonmuscle actin mRNAs suggests an unusually long untranslated region. Since tubulin and actin polypeptides are internal structural proteins, one would expect them to be synthesized only on free polysomes. Translation of mRNA derived directly from a purified membrane fraction or by puromycin release from that fraction, however, showed the synthesis of a small proportion of these proteins on polysomes that are membrane-associated. Peptide mapping has in all cases confirmed the identity of the products of cell-free synthesis with authentic alpha-tubulin, beta-tubulin and actin. Approximately 67% of the alpha- and 13% of the beta-tubulin chains produced by in vitro translation are competent for co-assembly into microtubules with added carrier microtubule protein.
编码α-和β-微管蛋白的信使核糖核酸已从鸡胚脑中分离出来。虽然这两种微管蛋白亚基的信使核糖核酸在天然凝胶上已得到分辨，但根据在含有甲基汞的变性凝胶上的迁移率判断，它们的分子量非常相似（650,000道尔顿）。β-和γ-肌动蛋白的信使核糖核酸也已在天然凝胶上得到分辨，但在变性条件下迁移时呈现为一个未分辨的峰（分子量650,000 - 700,000道尔顿）。由于非肌肉型肌动蛋白比α-和β-微管蛋白小得多，鸡非肌肉型肌动蛋白信使核糖核酸的大尺寸表明其非翻译区异常长。由于微管蛋白和肌动蛋白多肽是内部结构蛋白，人们可能会预期它们仅在游离多核糖体上合成。然而，直接从纯化的膜组分中获得的信使核糖核酸的翻译，或通过从该组分中用嘌呤霉素释放来进行的翻译，显示在与膜相关的多核糖体上合成了一小部分这些蛋白质。肽图谱分析在所有情况下都证实了无细胞合成产物与天然α-微管蛋白、β-微管蛋白和肌动蛋白的一致性。体外翻译产生的α-微管蛋白链中约67%以及β-微管蛋白链中约13%能够与添加的载体微管蛋白共同组装成微管。
