Looman A C, Bodlaender J, Comstock L J, Eaton D, Jhurani P, de Boer H A, van Knippenberg P H
Department of Biochemistry, University of Leiden, The Netherlands.
EMBO J. 1987 Aug;6(8):2489-92. doi: 10.1002/j.1460-2075.1987.tb02530.x.
In a lacZ expression vector (pMC1403Plac), all 64 codons were introduced immediately 3' from the AUG initiation codon. The expression of the second codon variants was measured by immunoprecipitation of the plasmid-coded fusion proteins. A 15-fold difference in expression was found among the codon variants. No distinct correlation could be made with the level of tRNA corresponding to the codons and large differences were observed between synonymous codons that use the same tRNA. Therefore the effect of the second codon is likely to be due to the influence of its composing nucleotides, presumably on the structure of the ribosomal binding site. An analysis of the known sequences of a large number of Escherichia coli genes shows that the use of codons in the second position deviates strongly from the overall codon usage in E. coli. It is proposed that codon selection at the second position is not based on requirements of the gene product (a protein) but is determined by factors governing gene regulation at the initiation step of translation.
在一个lacZ表达载体（pMC1403Plac）中，所有64个密码子都被引入到AUG起始密码子下游3'端的紧邻位置。通过对质粒编码的融合蛋白进行免疫沉淀来检测第二个密码子变体的表达。在密码子变体之间发现了15倍的表达差异。无法将其与对应密码子的tRNA水平建立明确的相关性，并且在使用相同tRNA的同义密码子之间观察到了很大差异。因此，第二个密码子的作用可能是由于其组成核苷酸的影响，大概是对核糖体结合位点结构的影响。对大量大肠杆菌基因的已知序列分析表明，第二个位置密码子的使用与大肠杆菌的整体密码子使用情况有很大偏差。有人提出，第二个位置的密码子选择不是基于基因产物（一种蛋白质）的需求，而是由翻译起始步骤中控制基因调控的因素决定的。
