生化1308第1組rna修飾

PosttranscriptionalModificationofRNA

RNA轉錄后的修飾1308班第一團隊主講：芮煜華組員：陳丹雷、周趙沁、蘇葉、邵堯力、

張楠、張曉君、穆蘭2015-03-11ContentrRNA的修飾tRNA的修飾mRNA的修飾RNA轉錄后修飾總結1.rRNA的轉錄后修飾ModificationofrRNA1.1OutlineConsistofrRNAandProteinProteinbiosyntheticmachinery.Ribosomes1.2rRNAModificationinProkaryotesCell1.3rRNAModificationinEukaryoticCell1.4ComparisonMatureRNAs1.2rRNAModificationinProkaryoticCellPre-rRNAtranscript(30S)①Methylatedatspecificbases③NucleasesreleasefinalproductsRNaseIIIRNaseERNaseP(bacteria)②CleavageliberatesrRNAs&tRNA(s)Intermediates1.3rRNAModificationinEukaryoticCellPre-rRNAtranscript(45S)②Cleavageproducesthe18S,5.8S,and28SrRNAs；MaturerRNAs①Methylatedmethylatedatmorethan100ofits14,000nucleotides*The5SrRNAisproducedseparately:byRNApolIII(vertebrates)snoRNAssmallnucleolarRNAs1.4ComparisonProkaryotes(Bacteria)Eukaryotic(Vertebrates)PrecursorSteps

MethylatedCleavagesiteSpecificRNAs30Spre-rRNA45Spre-rRNASinglepre-RNATwopre-RNAs23S16S5S28S18S5.8S/5S32Atspecificbasesatmorethan100basesDeterminedbyDeterminedbyRNaseIII,RNaseP,RNaseEsnoRNAs&RNaseNotmentionedsnoRNA2.tRNA的轉錄后修飾ModificationoftRNA2.1Outline5’cleavage3’cleavageCCAadditionbasemodificationsplicingMaturetRNAPrimarytranscript2.2ProcessofModificationIntermediateMaturetRNAPrimarytranscriptRNasePcutRNaseDcut5’cleavage3’cleavageCCAadditionbasemodificationSplicingnucleaseNucleotidyltransferases*Nucleotidyltransferases核苷酸轉移酶14-nucleotideintron2.3ModificationofBases二氫尿苷假尿苷DφUridine尿苷甲基化鳥苷mGuanosine鳥苷5－Methylcytosine（mC）甲基化胞苷Cytosine胞苷m2.4EffectsonfunctionoftRNAEffectsonfunctionoftRNA3D-structureStabilizationEfficiencyandhighfidelityoftranslation3.mRNA的轉錄后修飾ModificationofmRNAOutlineProkaryoticmRNAisgenerallyidenticaltoitsprimarytranscript.EukaryoticmRNAisextensivelymodifiedbothco-andposttranscriptionally.OverviewoftheprocessingofaeukaryoticmRNAPrimarytranscriptionreleasehn-RNA,alsoknownaspre-RNA.Allmodificationsoccurafterward.3.1mRNA——5’端加帽5’“Capping”3.1.1Structureof5’CappingS-腺苷蛋氨酸S-腺苷同型半胱氨酸3.1.2MechanismofCappingPhosphohydrolase磷酸水解酶①Removalofthephosphorylgroupfromthe5’-tri-phosphateofthepre-RNAGuanylyltransferase鳥苷酰轉移酶②AdditionofGMPGTP→PPi+GMPGuanylyl-7-methyltransferase鳥嘌呤-7-甲基轉移酶③MethylationoftheterminalGoccursinthecytosol2’-O-methyltransferase2’甲基轉移酶④AdditionalmethylationstepsOnlyinEukaryoticCell!!3.1.3Functionof5’CapFunctionofthe5’CapPreventsdegradationofmRNA.Permitsefficientinitiationoftranslation.Permitsefficientsplicing.Servesasasignalforexitingorenteringthenucleus.3.2mRNA——3’端加尾Additionofapoly-Atail多聚A尾3.2.1Structureofpoly-Atail3.2.2MechanismofPolyadenylationCPSFCstFRNApolIITranscribedpre-RNA②CPSFbindtheAAUAAAsequenceCstFbindtheGU-richorU-richsequence（AAUAAA：切割位點上游10-30nts處高度保守的信號序列；GU-/U-rich：切割位點下游20-40nts處）

PAP:多聚A聚合酶

PAB:多聚A結合蛋白①CPSF&CstFbindRNApolIICPSF:切割和多腺苷酸化特異性因子

CstF：cleavagestimulationfactor剪切刺激因子PAP,PABandcleavagefactorsCstFandcleavagefactorsadditionalPABCPSF③Original3’RNAcleavedoff；10Anucleotidesadded④FurtherAntsadded;

50-250(dependingonorganism)

PAB:‘molecularruler’OnlyinEukaryoticCell!!3.2.3PropertiesandFunctionPropertiesofPolyadenylationExistsinmostEukaryoticmRNAexcepthistone(組蛋白).Occursaftertranscription.UsesATPasthesubstrate.FunctionofPolyadenylationStabilizethemRNA.Facilitateitsexitfromthenucleus.Aidintranslation.3.3mRNA——前體剪接RNAsplicing3.3.1OutlinemRNAsplicingRequires2stepsoftransesterificationreaction(轉酯反應).RequiressnRNAs剪接（splicing）：將內含子剪切除去，外顯子連接起來的mRNA加工過程。5’-剪接供位（5’splicedonorsite）：恒定序列GU；3’-剪接受位（3’spliceacceptorsite）：恒定序列AG。分支點（branchsite）A：內含子的一個腺苷殘基。3.3.1Outline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個U或C的延伸+任意堿基+C，終止于AG；3’剪接部位上游的嘧啶富含區(qū)。3.3.2TransesterificationReaction第一步轉酯反應第二步轉酯反應兩次轉酯反應的結果Lariat，套索3.3.3RoleofsnRNAsinsplicingsnRNA：

smallnuclearRNA核小RNAU-rich參與剪接的snRNA:

U1、U2、U4、U5、U6剪接體(spliceosome)：

snRNAs+ProteinsnRNA+pro又稱snRNPs(核小核糖核蛋白顆粒)

剪接體的裝配需ATP供能3.3.4EffectofsplicesitemutationsSplicesitemutationInappropriatesplicingAbnormalproteinDiseases案例：β-地中海貧血是一種因β-珠蛋白產(chǎn)生缺陷所致的疾病,突變引起的β-珠蛋白mRNA不正確的剪接與某些β-地中海貧血病例有關.3.4mRNA——選擇性剪接Alternativesplicing3.4.1MechanismofAlternativesplicingEXON1EXON2EXON3EXON1EXON2EXON3EXON1EXON2EXON3EXON1EXON3EXON2ORpre-mRNAmoleculessplicedinalternativewaysmultiplevariationsofthemRNAmultiplevariationsofproteinproducts3.5mRNA——RNA編輯RNAediting3.5.1MechanismandExamples人載脂蛋白B基因（ApolipoproteinBgene）環(huán)境肝臟liver小腸intestineUAACAADeamination載脂蛋白apoB-100載脂蛋白apoB-48mRNAediting：inmammaliancellswhereindividualbasesubstitutioncauseachangeinthesequenceoftheprot