Sagiv精英名?？? Chapter2regulationofGeneExpressioninProkaryotesand 原核生物及 表達(dá)調(diào)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ChapterGeneExpressionPositiveandNegativeControlofGeneOperons:Coordina yRegulatedUnitsofGeneExpressionTheLactoseOperoninE.coli:InductionandCataboliteRepression2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ChapterOutlineThetryptophanOperoninE.coli:RepressionandAttenuationBacteriophageLambda:LysogenyorTemporalSequencesofGeneExpressionDuringPhageInfectionPost-TranslationalRegulatory2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? D’Hérelle’sDreamofTreatingDysenteryinHumansbyPhageTherapySagiv精英名?？? 一個(gè)畫餅充饑的夢(mèng)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? MicroorganismexhibitremarkablecapacitiestoadapttodiverseenvironmentalThisadaptabilitydependsinpartontheirabilitytoturnonandturnofftheexpressionofspecificsetsifgenesinresponsetochangesintheenvironment.Theexpressionofparticulargenesisturnedonwhentheproductsofthesegenesareneededforgrowth.Theirexpressionisturnedoffwhenthegenesproductsarenolongerneeded.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thesynthesisofgenetranscriptsandtranslationproductsrequirestheexpenditureofconsiderableenergy.Byturningofftheexpressionofgeneswhentheirproductsarenotneeded,anorganismcansaveenergyandcanutilizetheconservedenergytosynthesizeproducts izegrowthrate.What,then,arethemechanismsbywhichmicroorganismsregulategeneexpressioninresponsetochangesintheenvironment?2009-12-

原 表達(dá)調(diào) n/severaldifferentlevels:transcription,mRNAprocessing,mRNAturnover,translation,andpost-However,theregulatorymechanismswiththelargesteffectsonphenotypeactatthelevelof錄水平.Sagiv精英名校考 Basedonwhatisknownabouttheregulationoftranscription,thevariousregulationmechanismsseemtofitintotwogeneralcategories:Mechanismsthatinvolvetherapidturn-onandturn-offofgeneexpressioninresponsetoenvironmentalchanges.Regulatorymechanismsofthistypeareimportantinmicroorganismsbecauseofthefrequentexposureoftheseorganismstosuddenchangesinenvironment.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Mechanismsreferredtoasprepro-grammedcircuitsorcascadesofgeneexpression.Inthesecases,someeventtriggerstheexpressionofonesetof 應(yīng)機(jī)制Theproduct(s)ofoneormoreofthesefunctionsbyturningoffthetranscriptionofthefirstsetofgenesorturningonthetranscriptionofasecondsetofgenes.Then,oneormoreoftheproductsofthesecondsetactsbyturningonathirdset,andsoon.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inthesescases,thesequentialexpressionofgenesgeneticallypreprogrammed,andthegenescannotusuallybeturnedonoutofsequence.Suchpreprogrammedsequencesofgeneexpressionarewell edinprokaryotesandtheesthatattackthem.Forexample,whenalyticbacteriophageinfectsabacterium,theviralgenesareexpressedinapredeterminedsequence,andthissequenceisdirectlycorrelatedwiththetemporalsequenceofgene-productinvolvementinthereproductionandmorphogenenesisofthe 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Inmostoftheknownexamplesofgeneexpression,thecircuitryisForexample,duringviralinfections,someeventassociatedwiththepackagingoftheviralDNAorRNAintheproteincoatresetsthegeneticprogramsothatthepropersequenceofgeneexpressionoccursonceagainwhenaprogeny infectsanewhostcell(在 的過(guò)程中,有些事件與病 新的宿主細(xì)胞后一再發(fā)生)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Section1Constitutive,Inducible,andRepressibleGeneExpression 和抑制 表2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Genesthatspecifycellularcomponentsthatperformhousekee example,theribosomalRNAsandproteinsinvolvedinproteinsynthesis—areexpressed功能 —比如核糖體RNA和與蛋白合有關(guān)的蛋白—它們是 表達(dá)的Othergenesoftenareexpressedonlywhentheirproductsarerequiredforgrowth(其它 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Certaingeneproducts—suchastRNAmolecules,rRNAmolecules,ribosomalproteins,RNApolymerasesubunits,andenzymescatalyzingmetabolicprocessesthatarefrequentlyreferredtoascellular看家基因 gene”functions—essentialcomponentsofalmostalllivingGenethatspecifyproductsofthistypearecontinuallybeingexpressedinmostcells(編 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Suchgenearesaidtobeexpressedandarereferredtobeasconstitutivegenes(結(jié)構(gòu)基Othergeneproductsareneededforcellgrowthonlyundercertainenvironmentalconditions.Constitutivesynthesisofsuchgeneproductswouldbewasteful,usingenergythatcouldotherwisebeutilizedformorerapidgrowth(這些 合成是很浪費(fèi)的，所消耗的能量應(yīng)該用在更快速地生長(zhǎng)上2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Theevolutionofregulatorymechanismsprovideforthesynthesisofsuchgeneproductsonlywhenandwheretheyareneededwouldclearlyendowtheorganismsthatprocesstheseregulatorymechanismswithaselectiveadvantageoverorganismsthatlackthem.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Thisundoubtedlyexplainswhycurrentlyexistingorganisms,includingbacteriaes,exhibithighlyefficientmechanismsforthecontrolofgeneexpression.括細(xì)菌和，展現(xiàn)了非常高效的調(diào)控基2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Escherichiacoliandmostotherbacteriaarecapableofgrowthusingandoneofseveralcarbohydrates—forexample,glucose,sucrose,galactose,arabinose,andlactose—asanenergysource.Ifglucoseispresentintheenvironment,itwillbepreferentiallymetabolizedbyE.coli先代謝葡萄糖However,intheabsenceofglucose,E.colicellscangrowverywellonothercarbohy-2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Cellsgrowinginmediumcontainingsugarlactose,forexample,asthesolecarbonsourcesynthesizetwoenzymes,-galactosi-daseand–galactosidepermease,whichareuniquelyrequiredforthecatabolismof–galactosidepermeasepumpslactosethecell,where–galactosidasecleavesitintoglucoseandgalactose.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? CatabolismofNeitheroftheseenzymesisofanyusetoE.colicellsifnolactoseisavailabletothem(沒(méi)有乳2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thesynthesisofthesetwoenzymesrequiresconsiderableenergy(intheformofATPandGTP).Thus,E.colicellshaveevolvedaregulatorymechanismbywhichthesynthesisoftheselactose-catabolizingenzymesisturnedoninthepresenceoflactoseandturnedoffinits2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Innaturalenvironments(intestinaltractsandsewers),E.colicellsprobablyencounteranabsenceofglucoseandthepresenceoflactoserelativelyinfrequently.Therefore,theE.coligenesencodingtheenzymesinvolvedinlactoseutilizationareprobablyturnedoffmostofthetime.Ifcellsgrowingonacarbohydrateotherthanlactosearetransferredtomediumcontaininglactoseastheonlycarbonsource,theyquicklybegintosynthesizetheenzymesrequiredforlactoseutilization.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? (a)Inductionofthesynthesisofenzymesrequiredfortheutilizationoflactoseasanenergysource,(b)Repressionofthesynthesisoftheenzymesrequiredforthebiosynthesisoftryptophan,bothinE.coli.Notethatlowlevelsofenzymesynthesisoccurwhetherthemetabolitesarepresentorabsent.2009-12- 原 表達(dá)Sagiv精英名?？? Thisprocessofturningontheexpressionofgenesinresponsetoasubstanceintheenvironmentiscalledinduction(誘導(dǎo)).Geneswhoseexpressionisregulatedinthismannerarecalledinduciblegenes(可誘導(dǎo)基因);theirproducts,ifenzymes,arecalledinducibleenzymes(可誘導(dǎo)酶).Enzymesthatareinvolvedincatabolic(degradative)pathways,suchasinlactose,galactose,orarabinoseutilization,arecharacteristicallyinducible.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? InductionoccursatthelevelofInductionalterstherateofenzymesynthesis,nottheactivityofexistingenzymemolecules.Inductionshouldnotbeconfusedwith淆),whichoccurswhenthebindingofasmallmoleculetoanenzymeincreasestheactivityoftheenzyme,butdoesnotaffectits2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Bacteriacansynthesizemostoftheorganicmoleculesrequiredforgrowth,suchasaminoacids,purines,pyrimidines,andForexample,theE.coligenomecontainsfivegenesencodingenzymesthatcatalyze2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ThesefivegenesmustbeexpressedinE.colicellsgrowinginanenvironmentdevoidoftryptophaninordertoprovideadequateamountsofthisaminoacidforprotein 時(shí)候一定要表達(dá)，以提供足夠量的這種氨酸以滿足蛋白質(zhì)合成的需求WhenE.colicellsarepresentinanenvironmentcontainingenoughtryptophantosupportoptimalgrowth,thecontinuedsynthesisofthetryptophanbiosyntheticenzymeswouldbeawasteofenergy.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thus,aregulatorymechanismSagiv精英名?？? E.colithatturnsoffthesynthesisofthetryptophanbiosyntheticenzymeswhenexternaltryptophanisavailable(在可以利用Agenewhoseexpressionhasbeenturnedoffinthiswayissaidtobe“repressed”;theprocessiscalledrepression(阻遏).Whentheexpressionofthisgeneisturnedon,itissaidtobe“derepressed”;sucharesponseiscalledderepression(去阻遏2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) 精sthatarecomponentsofanabolic合成謝biosyntheticpathwaysoftenareRepression,likeinduction,occursatthelevelofRepressionshouldnotbeconfusedwithfeedbackinhibition,whichoccurswhentheproductofabiosyntheticpathwaybindstoandinhibitstheactivityofthefirstenzymeinthepathway,butdoesnotaffectthesynthesisoftheenzyme(阻遏不應(yīng)與反饋抑制相，生物合成途徑中的產(chǎn)物結(jié)合并抑2009-12-

原 表達(dá)調(diào) Sagiv

KeyInprokaryotes,genesthatspecifyhouse- functionssuchasrRNAs,tRNAs,andribosomalproteinsareexpressedconstitutively.OthergenesusuallyareexpressedonlywhentheirproductsareGenesthatencodeenzymesinvolvedincatabolicpathwaysoftenareexpressedonlyinthepresenceofthesubstratesoftheenzymes;theirexpressionisinducible.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 KeyGenesthatencodeenzymesinvolvedinanabolicpathwaysusuallyareturnedoffinthepresenceoftheendproductofthepathway;theirexpressionisrepressible.Althoughgeneexpressioncanberegulatedatmanylevels,transcriptionalregulationisthemostcommon.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? SectionPositiveandNegativeControlofGeneExpression表達(dá)的正調(diào)控和負(fù)調(diào)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Insomecases,theproductofaregulatorygeneisrequiredtoinitiatetheexpressionofoneormoregenes.Inothercases,theproductofaregulatorygeneisrequiredtoturnofftheexpressionofoneormoregenes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Theregulationofgeneexpression—induction,orturninggeneson,andrepression,orturninggenesoff—canbeplishedbybothpositivecontrolmechanismsandnegativecontrolBothmechanismsinvolveregulatorgenes—genesencodingproductsthatregulatetheexpressionofothergenes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inpositivecontrolmechanisms,theproductoftheregulatorgeneisrequiredtoturnontheexpressionofoneormorestructuralgenes,whereasinnegativecontrolmechanisms,theproductofregulatorgeneisnecessarytoshutofftheexpressionofstructuralgenes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? RecallthatageneisexpressedwhenRNApolymerasebindstoitspromoterandsynthesizesanRNAtranscriptthatcontainsthecodingregionofthegene.Theproductoftheregulatorygeneactsbybindingtothesitecalledtheregulatorproteinbindingsite(RPBS)adjacenttothepromoterofthestructuralgene(s).WhentheproductoftheregulatorgeneisboundattheRPBS,transcriptionofthestructuralgene(s)isturnedoffinanegativecontrolsystem,orturnedoninapositivecontrolsystem.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Theregulatorygeneproductsarecalledactivators(活化物)—becausetheyactivatethegeneexpression—inpositivecontroltheyrepressgeneexpression—innegativecontrolWhetherornotaregulatorproteincanbindtotheRPBSdependsonthepresenceorabsenceofeffectormolecules(效應(yīng)器分子)inthe2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Theeffectorsareusuallysmallmoleculessuchasaminoacids,sugar,andsimilarmetabolites.Theeffectormoleculesinvolvedininductionofgeneexpressionarecalledinducers(誘導(dǎo)物thoseinrepressionofgeneexpressionarecalledco-Theeffectormolecules(inducersandco-repressors)bindtoregulatorgeneproducts(activatorsandrepressors)andcausechangesinthethree-dimensionalstructuresoftheseproteins.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Conformationalchangesinproteinresultingfromthebindingofsmallmoleculesarecalledallosterictransitions(別構(gòu)轉(zhuǎn)換).Conformationalchangesinproteinsfrequentlyresultinalterationsintheiractivity.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inthecaseofactivatorsandrepressors,allosterictransitionscausedbythebindingofeffctormoleculesusuallyaltertheirabilitytobindtoregulatorproteinbindingsitesadjacenttothepromotersofthestructuralgenestheycontrol(無(wú)論是活化物 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Inanegative,induciblecontrolmechanism,thefreerepressorbindstotheRPBSandpreventsthetranscriptionofthestructuralgene(s)intheabsenceofinducer在負(fù)誘導(dǎo)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Wheninducerispresent,itisboundbytherepressor,andtherepressor/inducercomplexcannotbindtotheRPBS.WithnorepressorboundtotheRPBS,RNApolymerasebindstothepromoterandtranscribesthestructuralgene(s). 2009-12-

原 表達(dá)調(diào) theactivatorcannotbindtotheRPBSunlessinducerispresent,andRNApolymerasecannottranscribethestructuralgene(s)unlesstheactivator/inducercomplexisboundtotheRPBS(在正誘導(dǎo)調(diào)控機(jī)制中調(diào)控者 物，活化者，必須結(jié)合到RPBS上，RNA酶才能結(jié)合到啟動(dòng)子上，結(jié) 才能轉(zhuǎn)錄Thustranscriptionofthestructuralgenesisturnedononlyinthepresenceofinducer(結(jié)構(gòu)的轉(zhuǎn)錄僅在誘導(dǎo)物存在的情況下進(jìn)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inanegative,repressiblemechanism,transcriptionofthestructuralgene(s)occursintheabsenceoftheco-repressor,butnotinitspresence.Whentherepressor/co-repressorcomplexisboundtotheRPBS,itpreventsRNApolymerasefromtranscribingthestructuralInaabsenceofco-repressor,freerepressorcannotbindtothepromoterandtranscribethestructuralgenes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Inapositive,repressiblecontrolmechanism,theproductoftheregulatorgene,theactivator,mustbeboundtotheRPBSinorderforRNApolymerasetobindtothepromoterandtranscribethestructuralWhenco-repressorispresent,itformsacomplexwiththeactivatorprotein,andthisactivator/co-repressorcomplexisunabletobindtotheRPBS;consequently,RNApolymerasecannotbindtothepromoterandtranscribethestructuralgene(s).2009-12-

原 表達(dá)調(diào) i thesefourmechanismsofregulation,focusonthekeydifferencesbetween①Theregulatorgeneproduct,theactivator,participatesinturningongeneexpressioninapositivecontrolmechanism,whereastheregulatorgeneproduct,therepressor,isinvolvedinturningoffgeneexpressioninanegativecontrolmechanism(在正調(diào)控機(jī)制中，調(diào)控 產(chǎn)物，活化物參與開(kāi)放了 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ②Withbothpositiveandnegativecontrolmechanisms,whethergeneexpressionisinducibleorrepressibledependsonwhetherthefreeregulatorproteinortheregulatorprotein/effectormoleculecomplexbindstotheregulatorproteinbindingsite(無(wú)論是正調(diào)控還是負(fù)調(diào)控機(jī)制 表達(dá)都是可誘2009-12-

原 表達(dá)調(diào) Sagiv

KeyGeneexpressioniscontrolledbybothpositiveandnegativeregulatorymechanisms.Inpositivemechanisms,theproductofaregulatorgene,anactivator,isrequiredtoturnontheexpressionofthestructuralgene(s).Innegativecontrolmechanisms,theproductofaregulatorgene,arepressor,isnecessarytoturnofftheexpressionofthestructuralgene(s).2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? KeyActivatorsandrepressorsregulategeneexpressionbybindingtositesadjacenttothepromotersofstructuralgenes.Whetherornottheregulatorproteinscanbindtotheirbindingsitesdependsonthepresenceorabsenceofsmallfreeeffectormoleculesthatformcomplexwiththeregulatorproteins.Theeffectormoleculesarecalledinducersininduciblesystemsandco-repressorsinrepressible2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Section3Operon: RegulatedUnitsofGene子表達(dá)的協(xié)調(diào)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inprokaryotes,geneswithrelatedfunctionsoftenarepresentincoordina yregulatedgeneticunitscalledoperons. 常常存在于 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 The 子model,anegativemechanism,wasdevelopedin1961byandMonodtoexplaintheregulationofgenesrequiredforlactoseutilizationinE.coli.JacobandMonodproposedthatthetranscriptionofasetofcontiguousstructuralgenesisregulatedbytwocontrollingelements.Oneoftheelements,therepressorgene,encodesarepressor(阻遏物whichundertheappropriateconditions)bindtothesecondelement,theoperator(操作子).2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Transcriptionisinitiatedatpromoterlocatedjustupstream(5’)fromthecodingregionsofthestructuralgenesintheoperon Operatorregionsarecontiguouswithpromoterregions(操作子與啟動(dòng)子相鄰);sometimesoperatorsandpromotersevenoverlap,sharingashortDNAsequence(甚 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Operatorregionsareoftenlocatedbetweenthepromotersandstructuralgenesthattheyregulate(操作子常常位于啟動(dòng)子和它們調(diào)節(jié)的結(jié) 之間Thecompletecontiguousunitincludingthestructuralgenes,theoperator,andthepromoter,iscalledanoperon( 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Componentsofanoperon:oneormorestructuralgenes(three,SG1,SG2andSG3,areshown)andtheadjoiningoperator(O)andpromoter(P)sequences.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Whethertherepressorwillbindtotheoperatorandturnoffthetranscriptionofthestructuralgenesinanoperonisdeterminedbythepresenceorabsenceofeffectormolecules.阻遏物是否能夠結(jié)合到子的操作子上并關(guān)閉結(jié)構(gòu)的表達(dá)是有是否存在著效應(yīng)器2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inducibleoperonsandrepressibleoperonscanbedistinguishedfromoneanotherbydeterminingwhetherthenakedrepressorortherepressor/effectorcomplexisactiveinbindingtotheoperator 露的阻遏物或阻遏物/效應(yīng)分子復(fù)合物否可以結(jié)合到操作子2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Inthecaseofaninducibleoperon,thefreerepressorbindstotheoperator,turningofftranscription.Inthecaseofarepressibleoperon,thesituationisreversed.ThefreerepressorcannotbindtotheOnlytherepressor/effectormolecule(co-repressor)complexisactiveinbindingtotheoperator.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ThedifferencebetweenSagiv精英名校考 Thus,aninducibleoperonisturnedoffintheabsenceoftheeffecor(inducer)molecule,andarepressibleoperonisturnedonintheabsenceoftheeffector(co-repressor)molecule.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? AsinglemRNAtranscriptcarriesthecodinginformationofanentireoperon.Thus,themRNAsofopronsconsistingofmorethanonestructuralgenearemultigenic Forexample,thetryptophanoperonmRNAofE.colicontainsthecodingsequencesoffivedifferentgenes.Becausetheyareco-transcribed(由于它們是共轉(zhuǎn)錄的),allstructuralgenesinanoperonarecoordina yexpressed( 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Althoughthe tiesofdifferentgeneproductsneednottobethesame(becauseofdifferentefficienciesofinitiationoftranslationtherelativeamountofthedifferentpolypeptidesspecifiedbygenesinanoperonusuallyremainthesame,regardlessofthestateofinductionor子中 編碼的不同多肽的相對(duì)量 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Insomecases,thedifferentialuseoftranscriptionterminationsignalscanaltertheamountsofgeneproductssynthesized. 還有其它的調(diào)控方法嗎2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? KeyInbacteria,geneswithrelatedfunctionsfrequentlyoccurincoordina yregulatedunitscalledoperons.Eachoperoncontainsasetofcontiguousstructuralgenes,apromoter(thebindingsiteforRNApolymerase),andanoperator(thebindingsiteforaregulatoryproteincalledrepressor).Whenarepressorisboundtotheoperator,RNApolymerasecannottranscribethestructuralgenesintheoperon.Whentheoperatorisfreeofrepressor,RNApolymerasecantranscribetheoperon.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? SectionTheLactoseOperoninE.coli:InductionandCataboliteThestructuralgenesinlacoperonaretranscribedonlywhenlactoseispresentandglucoseisabsent. 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 JacobandMonadproposedtheoperonmodelontheirstudiesofthelactose(lac)operoninE.Thelacoperoncontainsapromoter(P),andoperator(O),andthreestructuralgenes,lacZ,lacY,andlacA,encodingtheenzymes-galactosidase,-galactosidepermease,and-galactosidetransacetylase,respectly.-galactosidepumpslactoseintothecell,where-galactosidasecleavesitintoglucoseandgalactose.Thebiologicalroleofthetransacetylasein2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ThelacoperonofE.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? oflactose2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 InJacobandMonad’smodel,thelacoperoncontainedasingleoperator(nowdesignatedHowever,twoadditionaloperators(O2O3)weresubsequentlyInitially,O2andO3werethoughttoplayveryminorroles.Then,Müller-Hillandcoworkersdemonstratedthatthedeletionofboth“minor”operatorshadalargeeffectontheleveloftranscriptionoftheoperon.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Morerecentstudieshaveshownthatefficientrepressionofthelacoperonrequiresthemajoroperator(O1)andatleastoneoftheminoroperators(O2orO3).Nevertheless,wewillfirstdevelopJacobandMonad’smodelofthelacoperonwithasingleoperator.Then,wewillextendthemodelandexaminethefunctionsofallthreeoperators. 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thelacoperonisanegativelycontrolledinducibleoperon;thelacZ,lacY,andlacAgenesareexpressedonlyinthepresenceofThelacregulatorgene,designatedtheIgene,encodesarepressorthatis360aminoacidslong.However,theactiveformofthelacrepressorisatetramercontainingfourcopiesoftheIgeneproduct.2009-12-

原 表達(dá)調(diào) 英Q/ tothelacoperator,whichinturnpreventsRNApolymerasefromcatalyzingthetranscriptionofthethreestructuralgens.AfewmolecularoflacZ,lacY,andlacAgeneproductsaresynthesizedintheuninducedstate,provingalowbackgroundlevelofenzymeactivity.Thisbackgroundactivityisessentialforinductionoflacoperonbecausetheinduceroftheoperon,allolactose(別乳糖isderivedfromlactoseinareactioncatalyzedby-2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Onceformed,allolactoseisboundbyrepressor,causingthereleaseoftherepressorfromtheoperator(別乳糖一旦形成，就會(huì)將阻遏物從操作子上解離下來(lái)Inthisway,allolactoseinducesthetranscriptionofthelacZ,lacY,andlacAstructuralgenes.ThelacIgene,thelacoperator,andthelacpromoterwereallinitiallyidentifiedgeneticallybytheisolationofmutantstrainsthatexhibitedalteredexpressionofthelacoperongenes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? MutationintheIgeneandtheoperatorfrequentlyresultinconstitutivesynthesisofthelacgeneproducts(I 致 產(chǎn)物的 表達(dá)2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? ThesemutationaredesignatedI-andOc,TheI-andOcconstitutivemutationcanbedistinguishednotonlybymapposition,butalsobytheirbehaviorinpartialdiploidsinwhichtheyarelocatedincisandtransconfigurationsrelatedtomutationsinlacstructuralgenes.I-和Oc構(gòu) 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Activitylevelsinwild-typebacterialhavebeensetat100unitsforboth-galactosidase(theproductofgeneZ)and-galactosidepermease(theproductofgeneY).TheAgeneanditsproduct-galactosidetransacetylasearenotshownforthesakeofbrevity.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Likemonoploidwild-type(I+P+O+Z+Y+A+)partialdiploids(alsocalledmerozygotes,部分合子)ofgenotypeF’I+P+O+Z+Y+A+/I+P+O+Z-Y-A-or F’I+P+O+Z-Y-A-/I+P+O+Z+Y+A+areinduciblefortheutilizationoflactoseasacarbonThewild-typealleles(Z+,Y+,andA+)ofthethreestructuralgenesaredominancetotheirmutantalleles(Z-,Y-,andA-).Thisdominanceisexpectedbecausethewild-typeallelesproducefunctionalenzymes,whereasthemutantallelesproducenoenzymesordefective(inactive)enzymes.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? PartialdiploidsofgenotypeI+P+O+Z+Y+A+/P+O+Z+Y+A+(I+/I-)arealsoinducibleforthesynthesisofthethreeenzymesspecifiedbythelacoperon.Thus,I+isdominanttoI-asexpected,becauseI+encodesafunctionalrepressormoleculeanditsI-allelespecifiesaninactiverepressor.ThedominanceofI+overI-alsoindicatesthattherepressorisdiffusible,becausetherepressorproducedbythelacI+alleleonthechromosomecanturnoffthelacstructuralgenesonbothoperonsinthecell.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Likewild-typecells,partialdiploidsofgenotypeF’I+P+O+Z+Y+A+/I+P+O+Z-Y-A-orgenotypeF’I+P+O+Z-Y-A-/I+P+O+Z+Y+A+areinduciblefor-galactosidase,-galactosidepermease,and-galactosidetransacetylase.Theinducibilityofthesegenotypesdemonstratesthatlacrepressor(I+geneproduct)controlstheexpressionofstructuralgeneslocatedeithercisortranstothelac+allele.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thelac+geneisdominanttolac-(a)Controlslacoperatorlocatedeithercis(b)ortrans(c)to表達(dá)調(diào) Sagiv精英名?？? Theoperatorconstitutive(Oc)mutationsactonlyincis;thatis,OcmutationaffecttheexpressionofonlythosestructuralgeneslocatedonthesameThecis-actingnatureofOmutationsislogicalgiventhefunctionoftheoperator.Omutationsshouldnotactintransiftheoperatoristhebindingsitefortherepressor;assuch,theoperatordoesnotencodeanyproduct,diffusibleorotherwise.Aregulatorgeneshouldactintransonlyifitspecifiesadiffusibleproduct.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Therefore,apartialdiploidofgenotypeI+P+O+Z-Y-A-/I+P+O+Z+Y+A+isinducibleforthethreeenzymesspecifiedbythestructuralgenesofthelacoperon,whereasapartialdiploidofgenotypeF’I+P+O+Z+Y+A+/I+P+O+Z-Y-A-synthesizestheseenzymesconstitutively(因此,當(dāng) 是F’I+P+O+Z-Y-A-/I+P+O+Z+Y+A+的時(shí)候， 子上的三個(gè)結(jié) 被誘導(dǎo)表達(dá) 的時(shí)候，這些酶 合成2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Activitylevelsinwild-typebacterialhavebeensetat100unitsforboth-galactosidase(theproductofgeneZ)and-galactosidepermease(theproductofgeneY).TheAgeneanditsproduct-galactosidetransacetylasearenotshownforthesakeofbrevity.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Theoperonactsonlyinthecis2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 Sagiv精英名?？? SomeoftheIgenemutations,designatedI-d,aredominanttothewild-typeallele(I+).I Thisdominanceresultsfromtheinabilityofheteromultimeresthatcontainbothwild-typeandmutantpolypeptidestobindtothe2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? OtherIgenemutations,thosedesignatedIs,causethelacoperontobeuninducible.InstrainscarryingtheseIsmutations,thelacstructuralgenescanusuallybeinducedtosomedegreewithhighconcentrationsofinducer,buttheyarenotinducedatnormalconcentrationsofinducer.2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Whenstudiedinvitro,themutantIspolypeptidesformstetramersthatbindtolacoperatorDNA.However,theyeitherdonotbindinducerorexhibitalowaffinityforinducer.Thus,theIsmutationsaltertheinducerbindingsiteofthelacrepressor.2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 PromotermutationsdonotchangeinducibilityofthelacInstead,theymodifythelevelsofgeneexpressionintheinducedanduninducedstatebychangingthefrequencyofinitiationoflacoperontranscription—thatis,theefficiencyofRNApolymerasebinding. 2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thelacpromoteractuallycontainstwoseparatecomponents:①TheRNApolymerasebinding②AbindingsiteforanotherproteincalledcataboliteactivatorproteinCAP，代謝活化者)thatpreventsthelacoperonfrombeinginducedinthepresenceofglucose. 2009-12-

原 表達(dá)調(diào) Sagiv精英名校考 CataboliteRepression(代謝抑制Thepresenceofglucosehaslongbeenknowntopreventtheinductionofthelacoperon,aswellasotheroperonscontrollingenzymesinvolvedincarbohydratecatabolism.Thisphenomenoncalledcataboliterepressionortheglucoseeffect,代謝抑制或葡萄糖效應(yīng)),assuresthatglucoseismetabolizedwhenpresent,inpreferencetoother,lessefficient,energy較低的能源而能夠被代謝2009-12-

原 表達(dá)調(diào) Sagiv精英名?？? Thecataboliterepressionthelacoperonandseveralother