Factors involved in initiation of haemoglobin synthesis can be phosphorylated in vitro
Factors involved in initiation of haemoglobin synthesis can be phosphorylated in vitro
复制标题
参与血红蛋白合成起始的因子可在体外被磷酸化
作者：
J. Traugh;S. Tahara;S. B. Sharp;B. Safer;W. Merrick
兔网织红细胞在含有放射性无机磷酸盐的营养培养基中孵育后，含有大量共价结合的磷酸盐。大约 65% 的磷酸盐附着在核糖体相关蛋白上，这些蛋白从核糖体释放到 0.5 M KCl 洗涤级分中；其余部分与核糖体蛋白1结合。高盐洗涤级分含有启动和维持蛋白质合成所需的各种蛋白质。为了分析磷酸化对蛋白质合成调节的影响，通过使用环 AMP 调节和环核苷酸非依赖性蛋白激酶，检查了从兔网织红细胞中纯化的起始因子的磷酸受体活性。在这里，我们描述了先前显示参与血红蛋白合成起始的两个因子的磷酸化。 IF-MP（Met-tRNAf 结合因子）和 IF-M2A（核糖体依赖性 GTP 酶活性）均由从兔网织红细胞中分离的环核苷酸独立蛋白激酶修饰。起始因子 IF-M1（参考文献 2）、IF-M2Bα（参考文献 3）、IF-M2Bβ（参考文献 3）、IF-M3（参考文献 4）和 IF-M4（参考文献 5）不会被该酶磷酸化。
RABBIT reticulocytes, after incubation in a nutritional medium with radioactive inorganic phosphate, contain a significant amount of covalently bound phosphate. Approximately 65% of this phosphate is attached to ribosome-associated proteins which are released into the 0.5 M KCl wash fraction from ribosomes; the remainder is bound to ribosomal protein1. The high salt wash fraction contains various proteins required for the initiation and maintenance of protein synthesis. To analyse the effects of phosphorylation on the regulation of protein synthesis, purified initiation factors from rabbit reticulocytes have been examined for phosphate-acceptor activity through the use of cyclic AMP-regulated and cyclic nucleotide-independent protein kinases. Here we describe the phosphorylation of two factors previously shown to be involved in the initiation of haemoglobin synthesis. Both IF-MP, the Met-tRNAf binding factor, and IF-M2A, a ribosome-dependent GTPase activity, are modified by a cyclic nucleotide-independent protein kinase isolated from rabbit reticulocytes. Initiation factors IF-M1 (ref. 2), IF-M2Bα (ref. 3), IF-M2Bβ (ref. 3), IF-M3 (ref. 4) and IF-M4 (ref. 5) are not phosphorylated by this enzyme.