chapter6-原核基因表達(dá)調(diào)控3-3

Chapter6RegulationofGeneexpressioninprocaryoticcells6.1Principlesoftranscriptionalregulation6.2lacoperon6.3trpoperon6.4Riboswitches6.5Phageλstrategy6.6ControloftranslationandDNArearrangement

6.5噬菌體裂解和溶源化的調(diào)控

Phagestrategies:lyticcascadesandlysogenicrepressionReference:Chapter27,GENESXFigure12.1Lyticdevelopmentinvolvesthereproductionofphageparticleswithdestructionofthehostbacterium,butlysogenicexistenceallowsthephagegenometobecarriedaspartofthebacterialgeneticinformation.lgenome48,514bp,dsDNA,有粘性末端:或環(huán)化,游離的;或以線狀原噬菌體態(tài)整合在寄主基因組上Figure12.11Thelambdamapshowsclusteringofrelatedfunctions.Thegenomeis48,514bp.5.5.2l裂解生長過程中的基因表達(dá)1.N,Cro首先被轉(zhuǎn)錄(earlygene)PL向左轉(zhuǎn)錄N,(N:抗終止因子)PR向右轉(zhuǎn)錄CroPL和PR控制的后早期基因(delayedearlygene)的表達(dá)轉(zhuǎn)錄出CII,CIII以及與復(fù)制有關(guān)的基因O,P,裂解基因Q.3.晚期基因(lategene)的表達(dá)通過Q基因的產(chǎn)物控制的:頭,尾蛋白基因的轉(zhuǎn)錄,為的成熟包裝提供必要的蛋白質(zhì).(Q蛋白類似于N,有抗終止作用)Figure12.13LambdaDNAcircularizesduringinfection,sothatthelategeneclusterisintactinonetranscriptionunit.LambdaimmediateearlyanddelayedearlygenesareneededforbothlysogenyandthelyticcycleLambdahastwoimmediateearlygenes,Nand

cro,whicharetranscribedbyhostRNApolymerase.N

isrequiredtoexpressthedelayedearlygenes.Threeofthedelayedearlygenes(cII,cIII,Q)

areregulators.LysogenyrequiresthedelayedearlygenescII-cIII.Thelyticcyclerequirestheimmediateearlygenecro

andthedelayedearlygeneQ.Figure12.10Thelambdalyticcascadeisinterlockedwiththecircuitryforlysogeny.5.5.3l溶源途徑裂解途徑特征是lDNA迅速復(fù)制，極大局部基因進(jìn)行表達(dá)，頭,尾蛋白產(chǎn)生后lDNA進(jìn)行包裝，寄主細(xì)胞裂解，l釋放.溶源途徑相反，只表達(dá)一個(gè)小的區(qū)段,以原噬菌體狀態(tài)整合在寄主染色體上.Aplaque

isanareaofclearinginabacteriallawn.Itiscreatedbyasinglephageparticlethathasundergonemultipleroundsoflyticgrowth.Aclearplaque

isatypeofplaquethatcontainsonlylysedbacterialcells.Figure12.15Wild-typeandvirulentlambdamutantscanbedistinguishedbytheirplaquetypes.Figure12.14Thelambdaregulatoryregioncontainsaclusteroftrans-actingfunctionsandcis-actingelements.6.5.3.1ThecIIandcIIIgenesareneededtoestablishlysogeny·ThedelayedearlygeneproductscIIandcIIIarenecessaryforRNApolymerasetoinitiatetranscriptionatthepromoterPRE,Pint(cIIactsdirectatthepromoterandcIIIprotectscIIfromdegradation.)TranscriptionfromPREleadstosynthesisofrepressorandalsoblocksthetranscriptionofcro.Pint:

leadstosynthesisof

Int(整合酶).cIIpromoteslysogenyinanother,indirectmanner.ItsponsorstranscriptionfromapromotercalledPanti-Q,whichislocatedwithintheQgene.antisensemRNA

ThecII-cIII

pairofregulatorsisneededtoestablishthesynthesisofrepressor.cII-cIII

是cI

合成的正調(diào)控因子,作用位點(diǎn):PECro間接抑制

cII,cIII

的轉(zhuǎn)錄,直接阻止cI轉(zhuǎn)錄,是cI

合成的負(fù)調(diào)控因子Figure12.28RNApolymerasebindstoPREonlyinthepresenceofcII,whichcontactstheregionaround-35.·PREhasatypicalsequencesat–10and–35.·RNApolymerasebindsthepromoteronlyinthepresenceofcII.·cIIbindstosequencesclosetothe–35region.Figure12.27RepressorsynthesisisestablishedbytheactionofcIIandRNApolymeraseatPREtoinitiatetranscriptionthatextendsfromtheantisensestrandofcrothroughthecIgene.LysogenyrequiresseveraleventscII/cIIIcauserepressorsynthesistobeestablishedandalsotriggerinhibitionoflategenetranscription.Establishmentofrepressorturnsoffimmediateanddelayedearlygeneexpression.Repressorturnsonthemaintenancecircuitforitsownsynthesis.LambdaDNAisintegratedintothebacterialgenomeatthefinalstageinestablishinglysogeny.Figure12.30Acascadeisneededtoestablishlysogeny,butthenthiscircuitisswitchedoffandreplacedbytheautogenousrepressor-maintenancecircuit.6.5.3.2Lysogenyismaintainedbyrepressorprotein溶源化的維持–PM啟動(dòng)子的轉(zhuǎn)錄已產(chǎn)生的整合酶(int產(chǎn)物)使l整合,溶源化;溶源化的維持需要l的CI有一個(gè)低水平的轉(zhuǎn)錄,保持自身阻遏的循環(huán),通過PM(maintenancepromoter)完成RepressormaintainsanautogenouscircuitFigure12.16Lysogenyismaintainedbyanautogenouscircuit(upper).Ifthiscircuitisinterrupted,thelyticcyclestarts(lower).RepressorbindingatOLblockstranscriptionofgeneNfromPL.·RepressorbindingatORblockstranscriptionofcrobutalsoisrequiredfortranscriptionofcI.TherepressoranditsoperatorsdefinetheimmunityregionImmunityinphagesreferstotheabilityofaprophagetopreventanotherphageofthesametypefrominfectingacell.Itresultsfromthesynthesisofphagerepressorbytheprophagegenome.Figure12.14Thelambdaregulatoryregioncontainsaclusteroftrans-actingfunctionsandcis-actingelements.Figure12.16Lysogenyismaintainedbyanautogenouscircuit(upper).Ifthiscircuitisinterrupted,thelyticcyclestarts6.5.4表達(dá)調(diào)控的分子機(jī)制TheDNA-bindingformofrepressorisadimerFigure12.17TheN-terminalandC-terminalregionsofrepressorformseparatedomains.TheC-terminaldomainsassociatetoformdimers;theN-terminaldomainsbindDNA.Figure12.18Repressordimersbindtotheoperator.TheaffinityoftheN-terminaldomainsforDNAiscontrolledbythedimerizationoftheC-terminaldomains.Repressorusesahelix-turn-helixmotiftobindDNAThehelix-turn-helixmotifdescribesanarrangementoftwoahelicesthatformasitethatbindstoDNA,onefittingintothemajorgrooveofDNAandotherlyingacrossit.Figure12.20Lambdarepressor''sN-terminaldomaincontainsfivestretchesofa-helix;helices2and3areinvolvedinbindingDNA.Figure12.21Inthetwo-helixmodelforDNAbinding,helix-3ofeachmonomerliesinthewidegrooveonthesamefaceofDNA,andhelix-2liesacrossthegroove.TherecognitionhelixdeterminesspecificityforDNAFigure12.22Twoproteinsthatusethetwo-helixarrangementtocontactDNArecognizelambdaoperatorswithaffinitiesdeterminedbytheaminoacidsequenceofhelix-3.CI和Cro是λ的兩種調(diào)節(jié)蛋白，都可與O結(jié)合，但親和力不同λ的生長途徑，是CI與Cro相互競爭O的過程。Figure12.24Eachoperatorcontainsthreerepressor-bindingsites,andoverlapswiththepromoteratwhichRNApolymerasebinds.TheorientationofOLhasbeenreversedfromusualtofacilitatecomparisonwithOR.RepressorCIdimer與O結(jié)合力大小順序：OR1>OR2>OR3,OL1>OL2>OL3Crodimer與O結(jié)合力大小順序：OR3>OR2>OR1,OL3>OL2>OL1CImRNAOR3OR2OR1CromRNANmRNAOL1OL2OL3PLPMPRCIdimer與O結(jié)合力大小順序：OR1>OR2>OR3,OL1>OL2>OL3Crodimer與O結(jié)合力大小順序：OR3>OR2>OR1,OL3>OL2>OL1Figure12.31ThelyticcascaderequiresCroprotein,whichdirectlypreventsrepressormaintenanceviaPRM,aswellasturningoffdelayedearlygeneexpression,indirectlypreventingrepressorestablishment.Whatdeterminesthebalancebetweenlysogenyandthelyticcycle?·ThedelayedearlystagewhenbothCroandrepressorarebeingexpressediscommontolysogenyandthelyticcycle.·ThecriticaleventiswhethercIIcausessufficientsynthesisofrepressortoovercometheactionofCro.Figure12.32Thecriticalstageindecidingbetweenlysogenyandlysisiswhendelayedearlygenesarebeingexpressed.IfcIIcausessufficientsynthesisofrepressor,lysogenywillresultbecauserepressoroccupiestheoperators.OtherwiseCrooccupiestheoperators,resultinginalyticcycle.導(dǎo)致溶源化因素營養(yǎng)耗竭M(jìn)OI值〔感染復(fù)數(shù)〕過高

lambdaimmediateearlyanddelayedearlygenesareneededforbothlysogenyandthelyticcycle

lyticcycledependsonantiterminationbyN

lysogenyismaintainedbythelambdarepressorcItherepressoranditsoperatorsdefinetheimmunityregion

lysogeny

prophagecmutantsKeytermsKeyConceptsChapter6RegulationofGeneexpressioninprocaryoticcells6.1Principlesoftranscriptionalregulation6.2lacoperon6.3trpoperon6.4Riboswitches6.5Phageλstrategy6.6ControloftranslationandDNArearrangement

6.6翻譯水平的調(diào)控對翻譯的調(diào)控通常發(fā)生在翻譯的起始或終止階段。翻譯調(diào)控既可在單順反子mRNA也可在多順反子mRNA上發(fā)生。翻譯起始調(diào)控的一個(gè)通常途徑是阻遏蛋白與mRNA翻譯起始位點(diǎn)AUG上游結(jié)合，從而阻止核糖體的結(jié)合。

Figure11.14AregulatorproteinmayblocktranslationbybindingtoasiteonmRNAthatoverlapstheribosome-bindingsiteattheinitiationcodon.6.6.1在翻譯水平上的自體調(diào)控AutonomousControl核糖體蛋白質(zhì)合成的自體調(diào)控Figure11.15ProteinsthatbindtosequenceswithintheinitiationregionsofmRNAsmayfunctionastranslationalrepressors.Figure11.17Genesforribosomalproteins,proteinsynthesisfactors,andRNApolymerasesubunitsareinterspersedinasmallnumberofoperonsthatareautonomouslyregulated.Theregulatorisnamedinred;theproteinsthatare