10. 基因转录后水平调控

基因转录后水平调控Post-transcriptional Processing of RNA

NucleusDNAPol II transcription Primary RNA transcript Nuclear processing Capping Splicing Polyadenylation Mature mRNA

Gene Expression:Multiple, Spatially and Temporally Distinct Steps Carried out by Distinct Cellular Machinery

Cytoplasm

Degradation

Mature mRNA Export Translation

Protein

- Regulation Can Be at Several Different Levels

- Dynamic Protein Association

Gene Expression: Complex Network of Coupled Interactions

Maniatis, T., and Reed , R. (2002 ). Nature 416 , 499-506.

All eukaryotic mRNAs are processed

mRNA transport

1. 5’加上m7GpppN 5 (capping戴“帽”)

Specific process for Pol II transcripts

Protection of mRNA from degradation Enhancement of mRNA’s translatability Transport of mRNA out of nucleus Proper splicing of pre-mRNA

2. 3’加“尾”(tailing)

① Facilitate to transport into cytosol ② Maintain mRNA stability

3. 拼接(splicing)

Increase mRNA diversity Splicing is mediated by snRNPs

Exons are similar in size

Introns are highly variable in size

GT-AG rule

GT-AG rule describes the presence of these constant dinucleotides at the first two and last two positions of introns of nuclear genes. Splice sites are the sequences immediately surrounding the exon-intron boundaries Splicing junctions are recognized only in the correct pairwise combinations

Splicing of pre-mRNA occurs in a “spliceosome” an RNA-protein complex

spliceosome(~100 proteins + 5 small RNAs)

pre-mRNA

spliced mRNA

The spliceosome is a large protein-RNA complex in which splicing of pre-mRNAs occurs.

染色质的空间变化

转录水平 转录后水平 翻译水平调控

转录

RNA的加工成熟

蛋白质加工水平翻译 mRNA的降解 多肽链的加工修饰 蛋白质的降解

基因转录后水平调控主要方式第一部分 mRNA structure/folding 第二部分 mRNA transport 第三部分 mRNA stability/degradation/decay 第四部分 mRNA editing 第五部分 mRNA methylation 第六部分 mRNA selective degradation 第七部分 miRNA/ncRNA (epigenetic section)

第一部分 RNA structure/foldingRibozyme Ribosome

Nobel prize 1989

Nobel prize 2009

The function of the RNA molecule depends on its folded structure

RNA functionsStructural e.g., rRNA, which is a major structural component of ribosomes BUT - its role is not just structural, also:

CatalyticRNA in the ribosome has peptidyltransferase activity Enzymatic activity responsible for peptide bond formation between amino acids in growing peptide chain Also, many small RNAs are enzymes "ribozymes”

Regulatory

Recently discovered important new roles for RNAs In normal cells: in "defense" - esp. in plants in normal development e.g., siRNAs, miRNA As tools: for gene therapy or to modify gene expression RNAi RNA aptamers

Hierarchical organization of RNA moleculesPrimary structure5’ to 3’ l

ist of covalently linked nucleotides, named by the attached base Commonly represented by a string S over the alphabet Σ={A,C,G,U}

Secondary StructureG G HAIRPIN LOOP A U U GBULGE C

C G U STEM A G A5’

G A INTERNAL LOOP A U C G C U U DANGLING ENDS3’

RNA “tertiary interactions”In addition to secondary structural interactions in RNA, there are also tertiary interactions.

Pseudoknot

Kissing hairpinsPseudoknot

Hairpin-bulge

StemInterior Loop

Single-Stranded

Bulge LoopJunction (Multiloop) Hairpin loop