RNA的 修饰

大肠杆菌染色体基因组共有tRNA基因约有60个
相同tRNA 不同tRNA
Polycistronic RNA
tRNA与rRNA 基因
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1.tRNA precursor processing in prokayote 加工酶
，识别5端二级结构
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process
RNaseD从3端修剪切去附 加核苷酸序列 →3’端成熟
2. tRNA modification in Eukaryotes.
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三、教学手段和方法
多媒体展示与讲述相结合 比较、归纳法教学
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8.1 tRNA precursor processing
1. tRNA precursor processing in prokaryote
the primary transcript.
Methylaiton and editing ect…..
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8.2.1 Capping / 加帽 P201
Capping is the process of adding a
derivative(m7G) of guanine nucleotide to the 5’ end of the pre-mRNA.
1.1 capping 1.2 tailing 1.3 mechanisms for intron splicing
难点
1.4 alternative splicing
1.5 RNA editing
2 . tRNA processing in prokaryotes
了解
1. rRNA processing both in prok. and Euk.
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Capping process8
Functions of the cap structure
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1. Helps prevent degradation
RNase
5’-3’ phospho diester bond
rRNA tRNA mRNA
Precursor processing
8.2 Post-transcription process in Prokaryotes
rRNA tRNA mRNA
Precursor processing
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三、学习目标要求
掌握 1 . mRNA processing in Eukaryotes
IInn eeuukkaarryyootteess,, ttrraannssccrriippttiioonn ttaakkeess ppllaaccee iinn tthhee
nnuucclleeuuss,,wwhheerreeaass ttrraannssllaattiioonn ttaakkeessppllaaccee iinn tthhee ccyyttooppllaassmm..
Chapter 8 RNA Modifications in Eukaryote and prokaryote
第8 RNA的 修饰
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一、地位与作用
Molecular mechanisms of every step in the central dogma.
DNA
Replication
DNA replication
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Interrupted gene → move introns → as template
Pre-mRNA
Splicing capping tailing editing methylation
mature mRNA
Prevent pre-RNA from digestion by RNase
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4. Helps remove the first intron
The first intron
RNA
DNA
RNA polymerase II
Cap is required for mRNA splicing, to occur
completly. Specifically, its presence is required for splicing of the first intron.
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8.2.2 Polyadenylation / 聚腺苷酸化P203
Polyadenylation is a modification process in which a string of about 250 adenine nucleotides is added to the 3’ end of the transcript.
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8.2 mRNA Modifications in Eukaryotes
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Question？ Thinking about… What is the difference of gene expression in prokaryote and eukaryote?
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8.2 mRNA Modifications in Eukaryotes
8.2.1 Capping 8.2.2 Polyadenylation 8.2.3 Splicing 8.2.4 mRNA Editing 8.2.5 mRNA recoding
8.1.1 加帽 8.1.2 聚腺苷酸化 8.1.3 剪接 8.1.4 mRNA编辑 8.1.5 m RNA 再编码
describe these alterations to the primary transcript.
The remove of nucleotides by both endonucleases
and exonucleases.
The addtion of nucleotides to the 5’-or 3’-ends of
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5’-5’ triphosphate bond
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Structure of the cap
7-methyl guanine nucleotide
5’-3’phosphodiester bond
methyl group 5’-5’ triphosphate bond
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intron
剪切和修剪 3’端均需添加-CCAOH 核苷修饰 内含子：酶促拼接
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2 .process
Rnase P cut
Rnase D cut
核酸内切酶（P）切去5端附加序列， 核酸外切酶(D)去除3附加序列， 胞苷酰转移酶在3’端加上CCA序列， RNase剪去内含子， 修饰酶修饰碱基。
TThheenn,,eevveenn wwhhiillee ttrraannssccrriippttiioonn iiss ssttiillll ooccccuurrrriinngg,,
rriibboossoommeessbbiinndd ttoo tthhee mmRRNNAA aanndd ttrraannssllaattee iitt ttoo mmaakkeepprrootteeiinn..
transcription,
Transcription
RNA processing,
translation，
Translation
RNA
Protein
control of gene expression,
etc…..
processed
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二、本章主要内容
8.1 Post-transcription process in Eukaryotes
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Concepts：
A primary transcript or pre-mRNA is an mRNA
that has been transcribed but is not yet ready for translation.
RNA processing is the collective term used to
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2. Helps transport into cytoplasm
Transcription occurs in the nucleus
Translation occurs in the cytoplasm
Cap structure helps the RNA transcript to pass through selective pores of the nuclear membrane and into the cytoplasm.
PPrrookkaarryyoottiiccggeenneeeexxpprreessssiioonn
FFiirrsstt,, RRNNAA ppoollyymmeerraassee ttrraannssccrriibbeess aa ggeennee,, oorr
sseett ooff ggeenneess,, iinn aann ooppeerroonn..
IInnttoo ccyyttooppllaassmmbbeeffoorree ttrraannssllaattiioonn ccaann bbeeggiinn,, oonn
tthhee wwaayy,, tthheessee ttrraannssccrriippttss uunnddeerrggoopprroocceessssiinngg..
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3. Enhances translation / 增强转译
Cap-binding protein
No translation occurs.
ribosome
In order to bind the ribosome, mRNA requires help from cap-binding protein. this protein requires the presence of the cap structure.
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Functions of the cap structure
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
4. Helps remove the first intron 帮助去除第一个内含子
RNase 5’-3’ phospho
diester bond
5’-5’ triphosphate bond
RNAs in the cell can be rapidly degraded by ribonucleases. However, these enzymes are generally not capable of degrading the triphosphate bond in the cap structure.
RNaseF切断tRNA前体的3’端；
碱基修饰，包括胞 苷酰转移酶在前体 的3’端加CCAOH等
CCA
RNaseP切断前体的5’端 →5’端成熟；
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1.tRNA precursor processing in eukaryote Structuret of tRNA Monocistronic RNA，构成gene cluster
This derivative is attached to the 5’ end
of the pre-mRNA by a 5’-5’ triphosphate bond linkage. The reaction is carried out by an enzyme called guanyltransferase(鸟 苷转移酶).
Capping takes place quite early.
5’-Cap
RNA
DNA
RNA polymerase II
Transcription of an mRNA occurs in the 5’ to 3’ direction. So, the 5’ end of the mRNA comes out first. Capping takes place when RNA pol transcriped 20—30nt, before the rest of the gene is transcribed.