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.

本过程详述了前体信使RNA（precursor messenger RNA）向成熟信使RNA（mRNA）的转化过程。前mRNA分子需经历三种主要的修饰过程。这些修饰包括5'端加帽、3'端多聚腺苷酸化和RNA剪接，它们均在RNA被翻译之前于细胞核内发生。5'端加帽：前mRNA的加帽过程涉及7-甲基鸟苷（m7G）的添加至5'端。此帽结构可保护初级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'端处理：RNA分子3'端的前mRNA处理涉及对其3'端的切割，随后添加约200个腺嘌呤残基以形成多聚(A)尾。随着多聚(A)尾的合成，它将与多聚(A)结合蛋白的多个拷贝结合，从而保护3'端免受核糖核酸酶的消化。剪接：RNA剪接是去除前mRNA中不编码蛋白质的内含子区域，并将剩余的外显子连接起来重新形成单一连续分子的过程。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。