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首页> 外文期刊>Molecular and Cellular Biology >Saccharomyces cerevisiae ribosomes recognize non-AUG initiation codons.
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Saccharomyces cerevisiae ribosomes recognize non-AUG initiation codons.

机译：酿酒酵母核糖体识别非AUG起始密码子。

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A series of Saccharomyces cerevisiae plasmids and mutant derivatives containing fusions of the Escherichia coli galactokinase gene, galK, to the yeast iso-1-cytochrome c CYC1 transcription unit were used to study the sequences affecting the initiation of translation in S. cerevisiae. When the CYC1 AUG initiation codon preceded the galK AUG codon and coding sequence and either the two AUGs were out of frame with each other or a nonsense codon was located between them, the expression of the galK gene was extremely low. Deletion of the CYC1 AUG and its surrounding sequences resulted in a 100-fold increase in galK expression. This dependence of galK expression on the elimination of the CYC1 AUG codon was used to select mutations in that codon. Then the ability of these altered initiation codons to serve in translational initiation was determined by reconstruction of the CYC1 gene 3' to and in frame with them. Initiation was found to occur at the codons UUG and AUA, but not at the codons AAA and AUC. Furthermore the codon UUG, when preceded by an A three nucleotides upstream, served as a better initiation codon than when a U was substituted for the A. The efficiency of translation from these non-AUG codons was quantitated by using a CYC1/galK protein-coding fusion and measuring cellular galactokinase levels. Initiation at the UUG codon was 6.9% as efficient as initiation at the wild-type AUG codon when preceded by an A three nucleotides upstream, but was over 10-fold less efficient when a U was substituted for that A. Initiation at AUA was 0.5% as efficient as at AUG. The effects of the sequences preceding the initiation codon are discussed in light of these results.
机译：使用一系列啤酒酵母质粒和突变体衍生物，其中包含大肠杆菌半乳糖激酶基因galK与酵母异-1-细胞色素c CYC1转录单位的融合体，用于研究影响啤酒酵母翻译起始的序列。当CYC1 AUG起始密码子在galK AUG密码子和编码序列之前，并且两个AUG彼此不合框架或位于它们之间的无义密码子时，galK基因的表达极低。 CYC1 AUG及其周围序列的删除导致galK表达增加100倍。 galK表达对CYC1 AUG密码子消除的这种依赖性用于选择该密码子中的突变。然后，通过将CYC1基因3'重建到它们并与其框内，来确定这些改变的起始密码子在翻译起始中起作用的能力。发现起始发生在密码子UUG和AUA处，而不发生在密码子AAA和AUC处。此外，密码子UUG（在上游3个核苷酸之前）是一个更好的起始密码子，比用U替代A时更好。这些非AUG密码子的翻译效率通过使用CYC1 / galK蛋白-编码融合蛋白并测量细胞半乳糖激酶水平。在上游有三个核苷酸的A之前，在UUG密码子上的启动效率是在野生型AUG密码子上的启动效率的6.9％，但是在用U代替A时，效率低10倍以上。在AUA上的启动效率是0.5 ％的效率与AUG相同。鉴于这些结果，讨论了起始密码子之前的序列的作用。

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