RNA生物合成（英文版）完整版

1

RNABIOSYNTHESIS

DNATranscriptionTranslationRNAProteinReversetranscriptionReplicationTheCentralDogmaThefundamentalprocessofinformationtransferincellsGeneexpression2023/10/27SXMU3Section1TranscriptionSection2RNAposttranscriptionalprocessingSection3RNAreplicationSection1TRANSCRIPTION1.1RNAsynthesisrequiresRNApolymeraseandDNAtemplateandactivatedprecursors1.2TranscriptioninProkaryotestakeplaceinthreephase1.3TranscriptioninEukaryotesismuchmorecomplexthanthatinProkaryotes2023/10/274SXMU.biochemistryandmolecularbiology1.1RNAsynthesisrequiresRNApolymeraseandDNAtemplateandactivatedprecursors2023/10/275SXMU.biochemistryandmolecularbiology

Template:oneoftheDNAstrands

Substrate:NTPs(ATP,GTP,CTP,UTP)

Enzyme:DNAdependentRNApolymerase(RNA-pol)

relyonthebasepairingrule

RNAchainispolymerizedin5’-3’direction

Otherfactors:suchasTF,ρfactorReplicationandtranscriptionaresimilarinsomerespects:

DNAservesastemplate

Nucleotidepolymerization

5’-3’directionRelyoncomplementarybasepairingrule

Form3’-5’phosphodiesterbondReplicationTranscriptionTemplateentirechromosomedsDNAOnlyparticulargenesaretranscribedatanyonetime.Onesegmentononestrand(asymmetrictranscription)SubstratedNTP(AGCT)NTP(AGCU)BasepairingA=TG≡CA=UT=AG≡CEnzymeDNA-polRNA-polPrimerRequireNotproductsProgenydsDNAmRNA,tRNA,rRNA…ComparisonoftranscriptionandreplicationTheTemplateforRNASynthesisOnlyparticulargenesorgroupsofgenesaretranscribedatanyonetime.OnlyoneDNAstrandactsasthetemplate2023/10/27SXMU9codingstrandtemplatestrandAsymmetrictranscription：5

3

3

5

templatestrandcodingstrandcodingstrandStructuregene1TranscriptiondirectiontranscriptiondirectiontemplatestrandStructuregene2Structuralgene:thesegmentsofDNA,canbetranscriptedtoRNA

TranscriptiongenerallyinvolvesonlyshortsegmentsofaDNAmolecule,andwithinthosesegmentsonlyoneofthetwoDNAstrandsservesasatemplate.

ThetemplatestrandofdifferentgenesisnotalwaysonthesamestrandofDNA.Thatis,inanychromosome,differentgenesmayusedifferentstrandsastemplate.

AsymmetrictranscriptionKeyterm1.2ThetranscriptioninprokaryotestakeplaceinthreephageInitiationElongationTermination

2023/10/27SXMU14(DNA-dependentRNApolymerase,transcriptase)E.colihasasingletypeofDNA-directedRNApolymerasethatsynthesizesalltypesofRNA.primerisnotrequired.Largeandcomplex:

(coreenzyme)

(holoenzyme)Initiationelongation

BindingofholoenzymetoinitiationregionSubunitMrFunctionα(2)37kDaDeterminewhichgenecanbetranscribedβ151kDaCatalyticsubunit,chaininitiationandelongationβ'156kDaDNAbindingσ70kDaRecognizeinitiationsiteRNApolymeraseinE.coliRifampicin(利福平):isanantibiotic，inhibitorofRNAsynthesisthatbindsspecificallytotheβsubunitofbacterialRNApolymerases,preventingtheinitiationoftranscription.BindingofRNApolymerasetoPromoter3'3'5'Promoter（啟動子）:TheDNAsequenceatwhichRNApolymerasebindstoinitiatetranscription.Itisalwayslocatedontheupstreamofagene.KeytermRNA-pol5'StructuralgeneRegionboundbyRNA-pol-50-40-30-20-101105'3'5'3'RNAstartsite?-35region-10regionTTGACAAACTGTTATAATPuATATTAPyPribnowboxConsensussequencePromoterinprokaryotesThemostcommonnucleotidessequence(recognitionsite)

(bindingsite)

ThePromoterofProkaryotesSize:40-60bp-35region(TTGACA):

asarecognitionsite

bindingwithRNA-polloosely-10region(TATAAT)Pribnowbox:bindingwithRNApolstably,involvinginunwinding(melting)DNAdoublehelixanddeterminingtheinitiation

Onceafewphosphodiesterbondsareformed,theσsubunitdissociates,leavingthecorepolymerasetocompletesynthesisoftheRNAmolecule.BindingofRNA-pol(holoenzyme)topromoter(closed/

opencomplex).2.UnwindingDNAduplex3.Formingphosphodiesterlinkagebetweenthefirsttwonucleotides.transcriptioninitiationcomplexⅠ.Initiation5’-pppG-OH+NTP→5’-pppGpN-OH+PPiFormatranscriptioninitiationcomplex:RNApol(

2

)-DNA-pppGpN-OH3

Featuresoftranscriptioninitiation:Holoenzymeisrequired(α2ββ'σ)Noprimer5’-endisGTPcommonlyFormingtranscriptioninitiationcomplexRNApol(

2

)-DNA-pppGpN-OH3

Ⅱ.Elongation?

Afterthepolymerasetranscribesapproximately10basepairs,theσ-subunitisreleased.Holoenzyme→coreenzyme?

ConformationofRNA-polchange,coreenzymeattachesandmovessmoothlyalongtheDNAtemplatecatalyzingthe

growthofRNAchainfrom5’to3’end.Formtranscriptionalcomplex(transcriptionbubble):RNA-pol(coreenzyme)-DNA-RNATranscriptionandtranslationproceedsimultaneousinprokaryotesRNApolymeraseRibosome

Transcriptionandtranslationproceedsimultaneousinprokaryotes2023/10/27SXMU30Featuresofelongation:①coreenzymeisresponsibleforelongation；②RNA

synthesisfrom5

-

to3

-direction；③readsDNA

templatefrom3

-to5

-

direction；④heteroduplexcontainingRNA-DNAof8bp；⑤alternatelyunwindingandrewindingofDNAtemplate.

Ⅲ.Termination

*RNApolstopsmovingalongDNAtemplate*transcriptRNAcomesofftranscriptioncomplex

1.Rhofactor-dependenttermination

2.Rhofactor-independenttermination1.Rhofactorconsistsof6units.Features:1)hasaffinityfortranscriptRNAespeciallyforpolyC2)hastwoenzymeactivities:

helicaseATPase2.Rhofactor-independenttermination:

*FeaturesoftranscriptRNA:self-complementarysequences:permittingtheformationofahairpinstructureorstem-loop.astringofUfollowingthehairpinstructure.Keytermsofthissection:*asymmetrictranscription*promoter2.1SomeRNAsarechemicallymodifiedaftertranscriptionalprocessing2.2EukaryoticmRNAsareextensivelyprocessedbynuclearEnzymesystem2.3RibosomalRNAsareprocessedfromlargerprecursors2.4TransferRNAsareextensivelyprocessedandmodified2.5RNAcanactasCatalysts2023/10/2736SXMU.biochemistryandmolecularbiologySection2RNAposttranscriptionalprocessing2023/10/27SXMU372.1SomeRNAsarechemicallymodifiedaftertranscriptionalprocessing2023/10/27SXMU382.2EukaryoticmRNAsareextensivelypr