生物化学资料：RNA转录后的修饰

1、Posttranscriptional Modification of RNARNA转录后的修饰,2015-03-11,Content,rRNA的修饰 tRNA的修饰 mRNA的修饰 RNA转录后修饰总结,1. rRNA的转录后修饰,Modification of rRNA,1.1 Outline,Consist of rRNA and Protein Protein biosynthetic machinery,Ribosomes,1.2 rRNA Modification in Prokaryotes Cell 1.3 rRNA Modification in Eukaryotic Cel

2、l 1.4 Comparison,1.2 rRNA Modification in Prokaryotic Cell,Pre-rRNA transcript (30S,RNase III,RNase E,RNase P,bacteria,1.3 rRNA Modification in Eukaryotic Cell,Pre-rRNA transcript (45S,The 5S rRNA is produced separately: by RNA pol III,vertebrates,snoRNAs small nucleolar RNAs,1.4 Comparison,30S pre-

3、rRNA 45S pre-rRNA,Single pre-RNA Two pre-RNAs 23S 16S 5S 28S 18S 5.8S / 5S,3 2,At specific bases at more than 100 bases,Determined by Determined by RNase III, RNase P, RNase E snoRNAs 50-250 (depending on organism) PAB : molecular ruler,Only in Eukaryotic Cell,3.2.3 Properties and Function,Propertie

4、s of Polyadenylation Exists in most Eukaryotic mRNA except histone(组蛋白). Occurs after transcription. Uses ATP as the substrate. Function of Polyadenylation Stabilize the mRNA. Facilitate its exit from the nucleus. Aid in translation,3.3 mRNA前体剪接,RNA splicing,3.3.1 Outline,mRNA splicing Requires 2 st

5、eps of transesterification reaction(转酯反应). Requires snRNAs,剪接（splicing）：将内含子剪切除去，外显子连接起来的mRNA加工过程。 5-剪接供位（5splice donor site）：恒定序列 GU； 3-剪接受位（3splice acceptor site）：恒定序列 AG。 分支点（branch site）A：内含子的一个腺苷残基,3.3.1 Outline,剪接的必需序列： 5剪接部位共有序列：AGGUAAGU； 3剪接部位共有序列：10个U或C的延伸+任意碱基+C，终止于AG； 3剪接部位上游的嘧啶富含区,3.3.2

6、Transesterification Reaction,两次转酯反应的结果,Lariat，套索,3.3.3 Role of snRNAs in splicing,snRNA： small nuclear RNA 核小RNA U-rich 参与剪接的snRNA: U1、U2、U4、U5、U6 剪接体 (spliceosome)： snRNAs + Protein snRNA+pro又称snRNPs(核小核糖核蛋白颗粒) 剪接体的装配需ATP供能,3.3.4 Effect of splice site mutations,案例：-地中海贫血是一种因-珠蛋白产生缺陷所致的疾病,突变引起的-珠蛋白m

7、RNA不正确的剪接与某些-地中海贫血病例有关,3.4 mRNA选择性剪接,Alternative splicing,3.4.1 Mechanism of Alternative splicing,EXON 2,OR,3.5 mRNARNA编辑,RNA editing,3.5.1 Mechanism and Examples,肝脏 liver,小肠 intestine,载脂蛋白 apoB-100,载脂蛋白 apoB-48,mRNA editing：in mammalian cells where individual base substitution cause a change in the sequence of the protein that is