中文摘要：

所有真核生物的rnRNA都在5’端被加帽，正确的加帽对mRNA的稳定性、出核及翻译调控具有重要意义。近年来，随着对Rail及其同源蛋白的酶活性的发现，引出一个对mRNA加帽过程质量控制机制的发现。研究表明，Rail及其同源蛋白可以将未被加帽（含5’端三磷酸基团）或未被正确加帽的mRNA转化成5’端含单磷酸基的RNA，使得它们可以被5＇-3’RNA外切酶降解。某些Rail的同源蛋白也具有5＇-3’RNA外切酶的活性，可以同时完成降解RNA的工作。Rail的同源蛋白在真核生物中广泛保守，提示这一机制普遍存在于真核生物中。

英文摘要：

All eukaryotic mRNAs are capped at their 5＇ end. Capping of mRNAs takes place co-transcriptionally and involves three steps. The intermediates of the capping process, as well as the uncapped 5＇ tri-phosphate RNA, are resistant to decapping and degradation by known factors, leading to the assumption that the capping process always proceeds to completion. This view was recently drastically changed. A novel family of enzymes, including the yeast proteins Rail, Dxo1/Ydr370C, and the mammalian protein DXO/Dom3Z, has been identified. These enzymes catalyze the conversion of the improperly capped mRNAs to 5＇ mono-phosphate RNA, allowing them to be degraded by 5＇-3＇ exoribonucleases. Several of these enzymes also possess 5＇-3＇ exoribonuclease activities themselves, and can single-handedly clear the improperly capped mRNAs. Studying of these enzymes has led to the realization that mRNA capping does not always proceed to completion, and the identification of an mRNA capping quality control mechanism in eukaryotes. In this paper, we briefly review recent advances in this area.