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1、李希分子醫(yī)學(xué)教育部重點(diǎn)實(shí)驗(yàn)室lixi@shmu.edu.cnTranscriptionandPost-transcriptionModificationPost-transcriptional ProcessingofRNAMakingendsofRNARNAsplicingPrimaryTranscriptPrimaryTranscript-theinitialmoleculeofRNAproduced---hnRNA（heterogenousnuclearRNA）Inprokaryotes,DNA→RNA→proteinincytoplasmcon
2、currentlyIneukaryotesnuclearRNA>>CpRNAProcessingofeukaryoticpre-mRNAHumandystrophingenehas79exons,spansover2,300-Kbandrequiresover16hourstobetranscribed!Forprimarytranscriptscontainingmultipleexonsandintrons,splicingoccursbeforetranscriptionofthegeneiscomplete--co-transcriptiona
3、lsplicing.TypesofRNAprocessingA)Cuttingandtrimmingtogenerateends:rRNA,tRNAandmRNAB)Covalentmodification:AddacapandapolyAtailtomRNAAddamethylgroupto2’-OHofriboseinmRNAandrRNAExtensivechangesofbasesintRNAC)Splicingpre-rRNA,pre-mRNA,pre-tRNAbydifferentmechanisms.TheRNAPolIICTDisreq
4、uiredforthecouplingoftranscriptionwithmRNAcapping,polyadenylationandsplicingThecouplingallowstheprocessingfactorstopresentathighlocalconcentrationswhensplicesitesandpoly(A)signalsaretranscribedbyPolII,enhancingtherateandspecificityofRNAprocessing.Theassociationofsplicingfactorsw
5、ithphosphorylatedCTDalsostimulatesPolIIelongation.Thus,apre-mRNAisnotsynthesizedunlessthemachineryforprocessingitisproperlypositioned.TimecourseofRNAprocessing5’and3’endsofeukaryoticmRNAAddaGMPMethylateitand1stfewnucleotidesCutthepre-mRNAandaddA’s5’-UTR3’-UTRCappingofpre-mRNAsCa
6、p=modifiedguaninenucleotideCapping=firstmRNAprocessingevent-occursduringtranscriptionCTDrecruitscappingenzymeassoonasitisphosphorylatedPre-mRNAmodifiedwith7-methyl-guanosinetriphosphate(cap)whenRNAisonly25-30bplongCapstructureisrecognizedbyCBC（cap-bindingcomplex）stablizethetrans
7、criptpreventdegradationbyexonucleasesstimulatesplicingandprocessingSometimesmethylatedSometimesmethylatedThecapisaddedafterthenascentRNAmoleculesproducedbyRNApolymeraseIIreachalengthof25-30nucleotides.GuanylyltransferaseisrecruitedandactivatedthroughbindingtotheSer5-phosphorylat
8、edPolIICTD.ThemethylgroupsarederivedfromS-adeno
