分子生物學(xué)課件第五章

Inprokaryotes,transcriptionproducesanearlyexactmRNAcopyoftheDNA,andthetranscriptisimmediatelytranslatedintoprotein.Ineukaryotes,aseriesofmodificationsoccurtomRNAduringandaftertranscription.在原核生物中，轉(zhuǎn)錄產(chǎn)生的mRNA幾乎是DNA的準(zhǔn)確拷貝，并且這一轉(zhuǎn)錄產(chǎn)物會(huì)立即被轉(zhuǎn)譯成蛋白質(zhì)。在真核生物中，轉(zhuǎn)錄時(shí)以及轉(zhuǎn)錄后會(huì)對(duì)mRNA進(jìn)行一系列修飾。Chapter5mRNAModificationsinEukaryotes

第5章真核生物mRNA的修飾Inprokaryotes,transcription5.1Capping5.2Polyadenylation5.3Splicing5.4mRNAEditing5.5Experiments5.1加帽5.2聚腺苷酸化5.3剪接5.4mRNA編輯5.5實(shí)驗(yàn)研究Chapter5mRNAModificationsinEukaryotes

第5章真核生物mRNA的修飾5.1Capping5.1加帽Chapter55.1Capping/加帽AnmRNAthathasbeentranscribedbutisnotyetreadyfortranslationiscalledapre-mRNA,oraprimarytranscript.Cappingistheprocessofaddingaderivativeofguaninenucleotidetothe5’endofthepre-mRNA.一條已經(jīng)轉(zhuǎn)錄出來但還沒有準(zhǔn)備好用于轉(zhuǎn)譯的mRNA稱為前體mRNA或初級(jí)轉(zhuǎn)錄本。加帽是在前體mRNA的5’末端加上一個(gè)鳥嘌呤核苷酸衍生物的過程。5.1Capping/加帽AnmRNAthaStructureofthecap/帽的結(jié)構(gòu)5’-3’phospho-diesterbond5’-5’triphosphatebondStructureofthecap/帽的結(jié)構(gòu)5RNApolymeraseIIDiscussedinChapter4RNApolymeraseIIDiscussedinCappingtakesplacequiteearly.5’-CapRNApolymeraseIIRNADNACappingtakesplacequiteearlCappingprocess/加帽過程Cappingprocess/加帽過程CTD:C-terminaldomainRNApolymeraseIIDNAMethyltransferaseGuanylyltransferaseRNAtriphosphataseCTD:C-terminaldomainRNApolyFunctionsofthecapstructure

帽結(jié)構(gòu)的功能1.Helpspreventdegradation

幫助防止降解2.Helpstransportintocytoplasm

幫助轉(zhuǎn)運(yùn)到細(xì)胞質(zhì)中3.Enhancestranslation/增強(qiáng)轉(zhuǎn)譯4.Helpsremovethefirstintron

幫助去除第一個(gè)內(nèi)含子Functionsofthecapstructure1.Helpspreventdegradation

幫助防止降解RNaseRNase5’-5’triphosphatebond5’-3’phosphodiesterbond5’-3’phosphodiesterbond1.Helpspreventdegradation

2.Helpstransportintocytoplasm

幫助轉(zhuǎn)運(yùn)到細(xì)胞質(zhì)中DiscussedinChapter72.Helpstransportintocytop3.Enhancestranslation/增強(qiáng)轉(zhuǎn)譯Cap-bindingproteinNotranslationoccurs.3.Enhancestranslation/增強(qiáng)轉(zhuǎn)RNApolymeraseIIRNADNA4.Helpsremovethefirstintron

幫助去除第一個(gè)內(nèi)含子ThefirstintronRNApolymeraseIIRNADNA4.HelAAAAAAA------AAAA5.2Polyadenylation/聚腺苷酸化Poly(A)tailPolyadenylationPre-mRNAPolyadenylation

isamodificationprocessinwhichastringofabout250adeninenucleotidesisaddedtothe3’endofthetranscript.AAAAAAA------AAAA5.2PPolyadenylationdoesnotoccuratthenaturalendPolyadenylationdoesnotoccurThepolyadenylationsignal/聚腺苷酸化信號(hào)AAAAAAA------AAAAPoly(A)tailPolyadenylationPre-mRNAPolyadenylationsignal

hasatypicaltypicalsequenceofAAUAAA.Thissequencegivesaninstructionas“tocutthemRNAabout20nucleotidesdownstream,nearaGU-richsequence”.

AAUAAAGUThepolyadenylationsignal/Thecleavagecomplex/切割復(fù)合體CleavagecomplexCPSF(cleavageandpolyadenylationspecificityfactor)CstF(cleavagestimulationfactor)CFI(cleavagefactorI)CFII(cleavagefactorsII)Thecleavagecomplex/切割復(fù)合體Poly(A)-BindingProteinPoly(A)-BindingProteinCTD:C-terminaldomainProteinsforcappingatCTDProteinsforpolyadenylationatCTDCTD:C-terminaldomainProteinsFunctionsofthepoly(A)tail

poly(A)尾的功能AAAAAAA------AAAAAAAAAAA---AAAAAAThemainfunctionofpoly(A)tailistoprotectthemRNAfromdegradationbyribonucleases.Functionsofthepoly(A)tail

Functionsofthepoly(A)tail

poly(A)尾的功能AAAAAAA------AAAAThereisalsosomeevidencethatthepoly-Atailisinvolvedin

splicingandenhancestranslationofmRNAs.Functionsofthepoly(A)tail

5.3Splicing/剪接Exons:Partsofagenethatareexpressedasprotein.Introns:Sequencesthatdonotcodeforproteinandinterruptthecodingregions.Splicing:Theprocessofremovingintronsfromapre-mRNA.5.3Splicing/剪接Exons:Par5.3.1TheBasicSplicingReaction

基本的剪接反應(yīng)5’

AG/GUAUGU…bodyofintron…UACUAAC-YAG

/3’SplicesitesinyeastSplicesites:Sequencesthatmarkthebeginningandendsofintronsandexons.5.3.1TheBasicSplicingReacThebasicsplicingreactionThebasicsplicingreaction5.3.2ProteinsinvolvedinSplicing

在剪接中發(fā)揮作用的蛋白質(zhì)Spliceosome:Thecollectionoffactors,especiallysnRNPs,thathelpwiththesplicingofintrons.5.3.2ProteinsinvolvedinSpsnRNPs:smallnuclearribonucleoproteinssnRNPsaresmallparticlesfoundinthenucleusandcontainbothproteinandRNA.snRNPsfunctioninginsplicing:U1,U2,U4,U5andU6.snRNPs:smallnuclearribonucl(推薦)分子生物學(xué)課件第五章(推薦)分子生物學(xué)課件第五章Nowshowing

mRNAsplicingFile:biophoto7\

LehningerPrinciplesofBiochemistry\mRNAsplicingNowshowing

mRNAsplicingFile:5.3.3Self-Splicing/自我剪接Tetrahymenathermophilia嗜熱四膜蟲

SplicingthatoccurswithoutthehelpofproteinsorsnRNPsiscalledself-splicing.5.3.3Self-Splicing/自我剪接TSelf-splicingofgroupIintronSelf-splicingofgroupIintroSelf-splicingofgroupIIintron

II類內(nèi)含子的自我剪接WithhelpofproteinsWithouthelpofproteinsSelf-splicingNormalsplicingSelf-splicingofgroupIIintr5.3.4Trans-Splicing/反式剪接MaturemRNAProteinRNApieceofseparateoriginDNA5.3.4Trans-Splicing/反式剪接Trans-Splicing/反式剪接Trans-Splicing/反式剪接5.3.5ReasonsforIntrons

內(nèi)含子存在的原因Introns-earlytheoryIntrons-latetheoryIntron:“WhyamIhere?”5.3.5ReasonsforIntrons

內(nèi)含子Intron-earlytheory/內(nèi)含子早現(xiàn)說E.coli“IheardsomebodysayE.colioncehadintrons.Isthattrue?”“Couldbe.Whoknows?!”Intron-earlytheory/內(nèi)含子早現(xiàn)說Intron-latetheory/內(nèi)含子后現(xiàn)說E.coli“Wearetheoneshavingintrons!

Weareproudofit.”Intron-latetheory/內(nèi)含子后現(xiàn)說EAlternativesplicing/可變剪接Alternativesplicing:akindofsplicingthatcanproducevariousproteinsfromonegene.Alternativesplicing/可變剪接ADrosophilaDscamgeneExon3Exon54.14.24.34.44.54.64.74.84.94.104.114.12Exon4Exon6Exon9AlternativeSplicingGoesMainstream可變剪接成為主流TheScientist,Volume17(24):28,Dec.15,2003DrosophilaDscamgeneExon3ExoAlternativesplicing/可變剪接Alternativesplicing