Bonetti B, Fu L, Moon J, Bedwell D M
Department of Microbiology, University of Alabama at Birmingham 35294, USA.
J Mol Biol. 1995 Aug 18;251(3):334-45. doi: 10.1006/jmbi.1995.0438.
In a recent study we found that the efficiency of translation termination could be decreased several hundred fold by altering the local sequence context surrounding stop codons in the yeast Saccharomyces cerevisiae. Suppression of termination was shown to be mediated by near-cognate tRNA mispairing with the termination codon. We have now examined in greater detail how the local sequence context affects the efficiency of translation termination in this organism. Our results indicate that the sequence immediately upstream of the termination codon plays a significant role in determining the efficiency of translation termination. An extended termination sequence (containing the stop codon and the following three nucleotides) was also found to be a major determinant of termination efficiency, with effects attributable to the fourth nucleotide being largely independent of the termination codon. For the UGA and UAA stop codons, the influence of the fourth position on termination efficiency (from most efficient to least efficient termination) was found to be G > U,A > C, while for the UAG codon it was U,A > C > G. These sequence-specific effects on the efficiency of translation termination suggest that polypeptide chain release factor (or another molecule that may play a role in translation termination, such as rRNA) recognizes an extended termination sequence in yeast. A previous study found a statistically significant bias toward certain tetranucleotide sequences (containing the stop codon and the first distal nucleotide) in several organisms. We found that tetranucleotide sequences most frequently used in yeast are among the most efficient at mediating translation termination, while rare tetranucleotide sequences mediate much less efficient termination. Taken together, our results indicate that upstream and downstream components of an extended sequence context act synergistically to determine the overall efficiency of translation termination in yeast.
在最近的一项研究中，我们发现通过改变酿酒酵母中终止密码子周围的局部序列环境，翻译终止效率可能会降低数百倍。结果表明，终止抑制是由近同源tRNA与终止密码子错配介导的。我们现在更详细地研究了局部序列环境如何影响该生物体中的翻译终止效率。我们的结果表明，终止密码子上游紧邻的序列在决定翻译终止效率方面起着重要作用。还发现一个扩展的终止序列（包含终止密码子及其后的三个核苷酸）是终止效率的主要决定因素，第四个核苷酸的影响在很大程度上独立于终止密码子。对于UGA和UAA终止密码子，发现第四个位置对终止效率的影响（从最有效的终止到最无效的终止）为G > U,A > C，而对于UAG密码子则为U,A > C > G。这些对翻译终止效率的序列特异性影响表明，多肽链释放因子（或另一个可能在翻译终止中起作用的分子，如rRNA）识别酵母中的扩展终止序列。先前的一项研究发现，在几种生物体中，某些四核苷酸序列（包含终止密码子和第一个远端核苷酸）存在统计学上显著的偏向性。我们发现酵母中最常用的四核苷酸序列是介导翻译终止最有效的序列之一，而罕见四核苷酸序列介导的终止效率则低得多。综上所述，我们的结果表明，扩展序列环境的上游和下游成分协同作用，以确定酵母中翻译终止的总体效率。
