Graves M C, Spremulli L L
Arch Biochem Biophys. 1983 Apr 1;222(1):192-9. doi: 10.1016/0003-9861(83)90516-7.
A method that permits the preparation of Euglena gracilis chloroplast 30 S ribosomal subunits that are largely free of endogenous initiation factors and that are active in the binding of fMet-tRNA in response to poly(A, U, G), has been developed. These 30 S subunits have been tested for activity in initiation complex formation with initiation factors from both procaryotes and eucaryotes. We have observed that Escherichia coli IF-2 binds fMet-tRNA nearly as well to Euglena chloroplast ribosomal subunits as it does to its homologous subunits. Neither wheat germ eIF-2 nor Euglena eIF-2A can bind fMet-tRNA efficiently to Euglena chloroplast or E. coli 30 S subunits although both are active with wheat germ 40 S ribosomal subunits. Euglena chloroplast 68 S ribosomes will also bind the initiator tRNA. Both E. coli IF-2 and E. coli IF-3 stimulate this reaction on chloroplast ribosomes with approximately the same efficiency as they do on their homologous ribosomes. E. coli IF-1 enhances the binding of fMet-tRNA to the chloroplast 68 S ribosomes when either IF-2 or IF-3 is limiting. The chloroplast ribosomes unlike E. coli ribosomes show considerable activity over a broad range of Mg2+ ion concentrations.
已开发出一种方法，可制备基本不含内源性起始因子且在响应聚（A，U，G）时能有效结合fMet-tRNA的纤细裸藻叶绿体30S核糖体亚基。这些30S亚基已针对与原核生物和真核生物起始因子形成起始复合物的活性进行了测试。我们观察到，大肠杆菌IF-2将fMet-tRNA与纤细裸藻叶绿体核糖体亚基结合的效果几乎与其同源亚基相同。小麦胚芽eIF-2和纤细裸藻eIF-2A都不能有效地将fMet-tRNA与纤细裸藻叶绿体或大肠杆菌30S亚基结合，尽管它们对小麦胚芽40S核糖体亚基都有活性。纤细裸藻叶绿体68S核糖体也会结合起始tRNA。大肠杆菌IF-2和大肠杆菌IF-3刺激叶绿体核糖体上的这一反应的效率与它们在同源核糖体上的效率大致相同。当IF-2或IF-3受到限制时，大肠杆菌IF-1会增强fMet-tRNA与叶绿体68S核糖体的结合。与大肠杆菌核糖体不同，叶绿体核糖体在很宽的Mg2+离子浓度范围内都表现出相当高的活性。
