Cap Analogs  (帽类似物)

“帽”结构（m7G[5']ppp[5']N，其中 N 可以是任何核苷酸）存在于由 RNA 聚合酶II生成的真核生物 mRNA 分子的5端。它通常由通过5-5三磷酸桥连接到 RNA 链5'端核苷酸上的一个7-甲基鸟苷部分组成。这种独特的帽结构在提供对5'端外切酶的抵抗力方面起着至关重要的作用，有助于保护mRNA避免被 5'端外切酶活性迅速降解。它参与了 mRNA 代谢的众多方面，如细胞内运输、剪接、细胞器定位、RNA 启动、翻译和 mRNA 转运。使用合成的二核苷酸类似物 m7G[5']ppp[5']G 是体外合成 5'端帽化的 mRNA 的最常用方法。

The “cap” structure (m7G[5']ppp[5']N, where N is any nucleotide) is present at the 5-end of eukaryotic mRNA molecules synthesized by RNA polymerase II. It typically consists of a 7-methylguanosine moiety attached via a 5-5 triphosphate bridge to the 5-terminal nucleoside of the RNA strand. The distinct cap structure plays a vital role in providing resistance to 5′‐exonuclease that helps to protect the mRNA from speedy degradation by 5′‐exonuclease activity. It has participated in numerous aspects of mRNA metabolism such as intracellular transport, splicing, subcellular localization, initiation of RNA, translation, and mRNA turnover. The use of the synthetic dinucleotide analog m7G[5']ppp[5']G has been the most common method for in vitro synthesis of 5-capped mRNAs. The presence of cap structure confers mRNA stability and enables efficient translation.