八肋游仆虫第二类肽链释放因子核定位信号分析

蛋白质合成终止过程中肽链释放因子负责终止密码子的识别.真核生物第二类肽链释放因子（eRF3）是一类GTP酶，协助第一类肽链释放因子（eRF1）识别终止密码子和水解肽酰 tRNA酯键.之前的研究表明,两类肽链释放因子在细胞核中发挥功能,参与蛋白质合成和纺锤体的组装.本研究根据软件预测结果,构建了一系列八肋游仆虫eRF3的截短型突变体，分析在其N端是否存在引导eRF3的核定位信号.结果表明，在eRF3的N端有两个区域（NLS1:23-36 aa 和 NLS2: 236-272 aa）可以引导eRF3进入细胞核中，而且这两个区域具有典型的核定位信号的氨基酸序列特征. eRF3的核定位与其作为一种穿梭蛋白的功能相一致，即参与细胞有丝分裂纺锤体的形成和无义介导的mRNA降解途径.

Eukaryotic Polypeptide Release Factor 3 from the Ciliate Euplotes octocarinatus Harbors a Nuclear Localization Signal Sequence

Polypeptide release factors are responsible for stop codon recognition during termination of protein biosynthesis. The class Ⅱ release factor, eukaryotic release factor 3 (eRF3), is a GTPase that promotes the class Ⅰ release factor, eukaryotic release factor 1 (eRF1), to recognize stop codons and hydrolyze ester bonds of peptidyl-tRNA. Previous study has shown that eRF3 and eRF1 function in the nucleus and are required for protein synthesis and spindle assembly. This study performed in silico prediction analyses and constructed a set of truncated forms of Euplotes octocarinatus eRF3 to determine whether the N-terminal extension might direct the subcellular localization of eRF3 in eukaryotic cells. The results indicated that two nuclear localization signal sequences (NLS1:23-36 aa and NLS2: 236-272 aa) located in the N-terminal domain of eRF3, contributed to eRF3 protein nuclear localization. Both NLSs shared structural similarity with classical nuclear localization signals. The localization of eRF3 in the nucleus is consistent with its function as a shuttle protein involved in the nonsense mediated mRNA decay pathway and/or spindle formation during mitosis.