生化1308第1组rna修饰

PosttranscriptionalModificationofRNA

RNA转录后的修饰1308班第一团队主讲：芮煜华组员：陈丹雷、周赵沁、苏叶、邵尧力、

张楠、张晓君、穆兰2015-03-11ContentrRNA的修饰tRNA的修饰mRNA的修饰RNA转录后修饰总结1.rRNA的转录后修饰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的转录后修饰ModificationoftRNA2.1Outline5’cleavage3’cleavageCCAadditionbasemodificationsplicingMaturetRNAPrimarytranscript2.2ProcessofModificationIntermediateMaturetRNAPrimarytranscriptRNasePcutRNaseDcut5’cleavage3’cleavageCCAadditionbasemodificationSplicingnucleaseNucleotidyltransferases*Nucleotidyltransferases核苷酸转移酶14-nucleotideintron2.3ModificationofBases二氢尿苷假尿苷DφUridine尿苷甲基化鸟苷mGuanosine鸟苷5－Methylcytosine（mC）甲基化胞苷Cytosine胞苷m2.4EffectsonfunctionoftRNAEffectsonfunctionoftRNA3D-structureStabilizationEfficiencyandhighfidelityoftranslation3.mRNA的转录后修饰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鸟苷酰转移酶②AdditionofGMPGTP→PPi+GMPGuanylyl-7-methyltransferase鸟嘌呤-7-甲基转移酶③MethylationoftheterminalGoccursinthecytosol2’-O-methyltransferase2’甲基转移酶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：切割位点上游10-30nts处高度保守的信号序列；GU-/U-rich：切割位点下游20-40nts处）

PAP:多聚A聚合酶

PAB:多聚A结合蛋白①CPSF&CstFbindRNApolIICPSF:切割和多腺苷酸化特异性因子

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

50-250(dependingonorganism)

PAB:‘molecularruler’OnlyinEukaryoticCell!!3.2.3PropertiesandFunctionPropertiesofPolyadenylationExistsinmostEukaryoticmRNAexcepthistone(组蛋白).Occursaftertranscription.UsesATPasthesubstrate.FunctionofPolyadenylationStabilizethemRNA.Facilitateitsexitfromthenucleus.Aidintranslation.3.3mRNA——前体剪接RNAsplicing3.3.1OutlinemRNAsplicingRequires2stepsoftransesterificationreaction(转酯反应).RequiressnRNAs剪接（splicing）：将内含子剪切除去，外显子连接起来的mRNA加工过程。5’-剪接供位（5’splicedonorsite）：恒定序列GU；3’-剪接受位（3’spliceacceptorsite）：恒定序列AG。分支点（branchsite）A：内含子的一个腺苷残基。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个U或C的延伸+任意碱基+C，终止于AG；3’剪接部位上游的嘧啶富含区。3.3.2TransesterificationReaction第一步转酯反应第二步转酯反应两次转酯反应的结果Lariat，套索3.3.3RoleofsnRNAsinsplicingsnRNA：

smallnuclearRNA核小RNAU-rich参与剪接的snRNA:

U1、U2、U4、U5、U6剪接体(spliceosome)：

snRNAs+ProteinsnRNA+pro又称snRNPs(核小核糖核蛋白颗粒)

剪接体的装配需ATP供能3.3.4EffectofsplicesitemutationsSplicesitemutationInappropriatesplicingAbnormalproteinDiseases案例：β-地中海贫血是一种因β-珠蛋白产生缺陷所致的疾病,突变引起的β-珠蛋白mRNA不正确的剪接与某些β-地中海贫血病例有关.3.4mRNA——选择性剪接Alternativesplicing3.4.1MechanismofAlternativesplicingEXON1EXON2EXON3EXON1EXON2EXON3EXON1EXON2EXON3EXON1EXON3EXON2ORpre-mRNAmoleculessplicedinalternativewaysmultiplevariationsofthemRNAmultiplevariationsofproteinproducts3.5mRNA——RNA编辑RNAediting3.5.1MechanismandExamples人载脂蛋白B基因（ApolipoproteinBgene）环境肝脏liver小肠intestineUAACAADeamination载脂蛋白apoB-100载脂蛋白apoB-48mRNAediting：inmammaliancellswhereindividualbasesubstitutioncauseachangeinthesequenceoftheprot