mRNA Processing

This process describes the conversion of precursor messenger RNA into mature messenger RNA (mRNA). The pre-mRNA molecule undergoes three main modifications. These modifications are 5' capping, 3' polyadenylation, and RNA splicing, which occur in the cell nucleus before the RNA is translated. 5' Capping: Capping of the pre-mRNA involves the addition of 7-methylguanosine (m7G) to the 5' end. The cap protects the 5' end of the primary RNA transcript from attack by ribonucleases that have specificity to the 3'5' phosphodiester bonds. 3' Processing: The pre-mRNA processing at the 3' end of the RNA molecule involves cleavage of its 3' end and then the addition of about 200 adenine residues to form a poly(A) tail. As the poly(A) tails is synthesised, it binds multiple copies of poly(A) binding protein, which protects the 3'end from ribonuclease digestion. Splicing: RNA splicing is the process by which introns, regions of RNA that do not code for protein, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule. Description adapted from Wikipedia: http://en.wikipedia.org/wiki/Post-transcriptional_modification Pathway adapted from http://www.reactome.org.

本过程阐述了前体信使RNA向成熟信使RNA（mRNA）的转化过程。在此过程中，前体mRNA分子经历了三种主要的修饰。这些修饰包括5'端加帽、3'端多聚腺苷酸化以及RNA剪接，这些过程均在RNA被翻译之前在细胞核内进行。5'端加帽：前体mRNA的加帽过程涉及7-甲基鸟苷（m7G）添加至5'端。该加帽结构能够保护初级RNA转录本的5'端免受具有3'5'磷酸二酯键特异性的核糖核酸酶的攻击。3'端加工：RNA分子3'端的前体mRNA加工涉及对其3'端的切割，随后添加约200个腺嘌呤残基以形成多聚腺苷酸尾巴。随着多聚腺苷酸尾巴的合成，它将结合多个多聚腺苷酸结合蛋白，从而保护3'端免受核糖核酸酶的降解。剪接：RNA剪接是去除前体mRNA中的内含子（不编码蛋白质的RNA区域），并将剩余的外显子连接起来重新形成单个连续分子的过程。本描述改编自维基百科：http://en.wikipedia.org/wiki/Post-transcriptional_modification。途径改编自http://www.reactome.org。