Looman A C, Laude M, Stahl U
Institut für Gärungsgewerbe und Biotechnologie, Berlin, FRG.
Yeast. 1991 Feb;7(2):157-65. doi: 10.1002/yea.320070209.
A set of 32 different codons were introduced in a lacZ expression vector (pPTK400) immediately 3' from the AUG initiation codon. Expression of the lacZ gene was determined in Saccharomyces cerevisiae by measuring the amount of beta-galactosidase fusion protein using immuno-gel electrophoresis. A 5.3-fold difference in expression was found among the various constructs. It was found that there was no preference for a certain nucleotide in any position of the second codon and there was no distinct correlation between the level of tRNA corresponding to any particular second codon and expression. No correlation could be found between the local secondary structure and expression. When the overall codon usage in yeast and the codon usage in the second position of the mRNA is compared, there is no obvious significant difference in preference. This indicates that in yeast, in contrast to Escherichia coli, the codon choice at the beginning of the mRNA does not deviate from the one further downstream and is determined by the requirements for optimal translation elongation. Important determinants of the optimal context for an initiation codon in yeast therefore must be located mainly 5' from this codon.
在一个lacZ表达载体（pPTK400）中，紧挨着AUG起始密码子的3'端引入了一组32种不同的密码子。通过免疫凝胶电泳测量β-半乳糖苷酶融合蛋白的量，来确定酿酒酵母中lacZ基因的表达。在各种构建体中发现表达存在5.3倍的差异。发现在第二个密码子的任何位置对特定核苷酸都没有偏好，并且对应于任何特定第二个密码子的tRNA水平与表达之间没有明显的相关性。局部二级结构与表达之间也没有相关性。当比较酵母中的总体密码子使用情况和mRNA第二个位置的密码子使用情况时，偏好上没有明显的显著差异。这表明在酵母中，与大肠杆菌不同，mRNA起始处的密码子选择与下游的密码子选择没有偏差，并且由最佳翻译延伸的要求决定。因此，酵母中起始密码子最佳上下文的重要决定因素必须主要位于该密码子的5'端。
