Mitra S K, Lustig F, Akesson B, Lagerkvist U
J Biol Chem. 1977 Jan 25;252(2):471-8.
An in vitro protein-synthesizing system completely dependent on added valine tRNA (valyl-tRNAval) and programmed with RNA from the phage MS2 has been used to investigate the incorporation into MS2 coat protein of valine from isoaccepting valyl-tRNAsval with the anticodons U AC (U represents 5-oxyacetic acid uridine monophosphate), GAC, and IAC in response to the four valine codons GUU, GUC, GUA, and GUG. By examining the incorporation of valine into NH2-terminal and internal positions of three tryptic peptides from the MS2 coat protein it has been established that these anticodons each recognize all four valine codons. We therefore conclude that under our conditions of in vitro protein synthesis the genetic code, as far as the valine codons are concerned, is operationally a two letter code, i.e. the third codon nucleotide has no absolute discriminating function.
一个完全依赖添加缬氨酸tRNA（缬氨酰 - tRNAval）且用噬菌体MS2的RNA编程的体外蛋白质合成系统，已被用于研究具有反密码子UAC（U代表5 - 氧乙酸尿苷单磷酸）、GAC和IAC的同功缬氨酰 - tRNAval中的缬氨酸，响应四个缬氨酸密码子GUU、GUC、GUA和GUG掺入MS2外壳蛋白的情况。通过检测缬氨酸掺入MS2外壳蛋白的三个胰蛋白酶肽段的氨基末端和内部位置，已确定这些反密码子各自识别所有四个缬氨酸密码子。因此我们得出结论，在我们的体外蛋白质合成条件下，就缬氨酸密码子而言，遗传密码在操作上是一个双字母密码，即第三个密码子核苷酸没有绝对的区分功能。
