Guanylyl transferase
DNA
RNA polymerase II
Proteins for polyadenylation at CTD
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Functions of the poly(A) tail poly(A)尾的功能
The main function of poly(A) tail is to protect the mRNA from degradation by ribonucleases.
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Drosophila Dscam gene
[drəusɔfilə]
Exon 4
Exon 6
Exon 9
Exon 3
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12
CFI (cleavage factor I)
CFII (cleavage factors II)
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Poly(A)-Binding Protein
CTD: C-terminal domain
Proteins for capping at CTD
Methyl transferase
RNA triphosphatase
Tetrahymena thermophilia [tetrəhaimənə]嗜热四膜虫 [θə:məfailiə]
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Self-splicing of group I intron
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Self-splicing of group II intron II 类内含子的自我剪接
Introns-late theory
A
Exon 2 3’
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Intron-early theory / 内含子早现说
E. coli
“I heard somebody say E. coli once had introns. Is that true?”
“Could be. Who knows?!”
5’-Cap
RNA DNA
RNA polymerase II
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Capping process / 加帽过程
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CTD: C-terminal domain
Methyl transferase
RNA triphosphatase
Guanylyl transferase
DNA
RNA polymerase II
Chapter 5 mRNA Modifications
in Eukaryotes 第5章 真核生物mRNA的修饰
In prokaryotes,
在原核生物中，转录产
transcription produces a 生的mRNA几乎是
nearly exact mRNA copy of DNA的准确拷贝，并且
AAAAAAA - - - - - - AAAA
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5.3 Splicing / 剪接
Exons: Parts of a gene that are expressed as protein. Introns: Sequences that do not code for protein and interrupt the coding regions. Splicing: The process of removing introns
5.1 加帽 5.2 聚腺苷酸化 5.3 剪接 5.4 mRNA编辑 5.5 实验研究
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5.1 Capping / 加帽
An mRNA that has been transcribed but is not yet ready for translation is called a pre-mRNA, or a primary transcript.
Capping is the process of adding a derivative of guanine nucleotide to the 5’ end of the pre-mRNA.
一条已经转录出来但 还没有准备好用于转 译的mRNA称为前体 mRNA或初级转录本。
加帽是在前体mRNA 的5’末端加上一个鸟 嘌呤核苷酸衍生物的 过程。
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2. Helps transport into cytoplasm 帮助转运到细胞质中
Discussed in Chapter 7
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3. Enhances translation / 增强转译
Cap-binding protein
No translation occurs.
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Functions of the cap structure 帽结构的功能
1. Helps prevent degradation 帮助防止降解
2. Helps transport into cytoplasm 帮助转运到细胞质中
3. Enhances translation / 增强转译
5’ AG/GUAUGU…body of intron…UACUAAC-YAG / 3’
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The basic splicing reaction
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5.3.2 Proteins involved in Splicing 在剪接中发挥作用的蛋白质
Spliceosome: The collection of factors, especially snRNPs, that help with the splicing of introns.
after transcription.
系列修饰。
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Chapter 5 mRNA Modifications
in Eukaryotes 第5章 真核生物mRNA的修饰
5.1 Capping 5.2 Polyadenylation 5.3 Splicing 5.4 mRNA Editing 5.5 Experiments
DNA Mature mRNA Protein
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Trans-Splicing / 反式剪接
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5.3.5 Reasons for Introns 内含子存在的原因
Introns-early theory
Intron: “Why am I here?”
U
G
Exon 1
G
5’
Intron
Pre-mRNA
Polyadenylation
AAAAAAA - - - - - - AAAA
Poly(A) tail
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Polyadenylation does not occur at the natural end
Pre-mRNA
Polyadenylation
AAAAAAA - - - - - - AAAA
AAAAAAA - - - - - - AAAA
AAAAAAA - - -
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Functions of the poly(A) tail poly(A)尾的功能
There is also some evidence that the poly-A tail is involved in splicing and enhances translation of mRNAs.
from a pre-mRNA.
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5.3.1 The Basic Splicing Reaction 基本的剪接反应
Splice sites: Sequences that mark the beginning and ends of introns and exons.
Splice sites in yeast
AAUAAA
GU
Polyadenylation
AAAAAAA - - - - - - AAAA
Poly(A) tail
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The cleavage complex / 切割复合体
Cleavage complex
CPSF (cleavage and polyadenylation specificity factor) CstF (cleavage stimulation factor)
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Structure of the cap / 帽的结构
5’-3’ phosphodiester bond
5’-5’ triphosphate bond
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RNA polymerase II
Discussed in Chapter 4
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Capping takes place quite early.
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Intron-late theory / 内含子后现说
E. coli
“We are the ones having introns! We are proud of it.”
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Alternative splicing / 可变剪接
Alternative splicing: a kind of splicing that can produce various proteins from one gene.
the DNA, and the transcript 这一转录产物会立即被
is immediately translated 转译成蛋白质。在真核
into protein. In eukaryotes, a series of modifications
生物中，转录时以及转