中文摘要：

蛋白质翻译终止过程中第一类肽链释放因子（eukaryotic polypeptide release factor,eRF1）识别终止密码子,水解肽酰-tRNA酯键,释放新生肽链,但eRF1识别终止密码子的机制尚不清楚。纤毛虫eRF1识别密码子的特异性为研究该机制提供了理想的材料。分析了赭纤虫（Blepharisma japonicum）eRF1的N端结构域中与密码子识别有关的关键的氨基酸。预测发现赭纤虫和酵母eRF1的一些与密码子识别有关的氨基酸被磷酸化修饰的几率很高,且二者磷酸化修饰的氨基酸位点有所差异。利用点突变方法向赭纤虫eRF1的N端引入与酵母eRF1一致的磷酸化位点时（N23S/D25E/A70S/Q115E）,其识别终止密码子的特异性发生改变,由UAA/UAG识别特异性转变为UAA/UAG/UGA三个密码子全识别。说明这些位点磷酸化可能参与调节eRF1识别终止密码子的功能。

英文摘要：

Eukaryotic polypeptide release factor eRF1 decodes the three stop codons and hydrolysis the ester bond of peptidyl-tRNA,leading to release of renascence polypeptide,however,the detailed molecular mechanism remains unknown.Variant codon species,such as ciliates,frequently exhibit altered stop codon recognition,which provide us model for elucidating the mechanism of stop codon recognition by eRF1.The key amino acids associated with codon recognition in N-terminal domain of Blepharisma japonicum eRF1（Bj eRF1）were analyzed in this study.We found that the score of phosphorylation of some amino acids in eRF1 fromBlepharisma and Saccharomyces cerevisiae（Sc eRF1）were relatively high,and modifying pattern of both eRF1 swere different.We introduced the phosphorylation site into Bj eRF1 according to Sc eRF1 pattern by using site-direct mutagenesis.The resulted mutant Bj eRF1（N23S/D25E/A70S/Q115E）could recognize three stop codons,suggesting these amino acids might be involved in regulation of stop codon recognition by eRF1.