Gene-X-ppt(Gene10-基因十)--Chapter12

Chapter12ExtrachromosomalReplicons12.1Introduction•plasmid–Circular,extrachromosomalDNA.–Itisautonomousandcanreplicateitself.•lysogenic–Theabilityofaphagetosurviveinabacteriumasastableprophagecomponentofthebacterialgenome.12.1Introduction•episome–AplasmidabletointegrateintobacterialDNA.•immunity–Inplasmids,theabilityofaplasmidtopreventanotherofthesametypefrombecomingestablishedinacell.12.2TheEndsofLinearDNAAreaProblemforReplication•SpecialarrangementsmustbemadetoreplicatetheDNAstrandwitha5′end.FIGURE01:Replicationcouldrunoffthe3’endofanewlysynthesizedlinearstrand,butcoulditinitiateata5’end?12.3TerminalProteinsEnableInitiationattheEndsofViralDNAs•stranddisplacement–AmodeofreplicationofsomevirusesinwhichanewDNAstrandgrowsbydisplacingtheprevious(homologous)strandoftheduplex.FIGURE02:AdenovirusDNAreplicationisinitiatedseparatelyatthetwoendsofthemoleculeandproceedsbystranddisplacement12.3TerminalProteinsEnableInitiationattheEndsofViralDNAs•Aterminalproteinbindstothe5′endofDNAandprovidesacytidinenucleotidewitha3′–OHendthatprimesreplication.FIGURE04:Adenovirusterminalproteinbindstothe5’endofDNAandprovidesaC-OHendtoprimesynthesisofanewDNAstrand12.4RollingCirclesProduceMultimersofaReplicon•Arollingcirclegeneratessingle-strandedmultimersoftheoriginalsequence.FIGURE05:Therollingcirclegeneratesamultimericsingle-strandedtailFIGURE07:Thefateofthedisplacedtaildeterminesthetypesofproductsgeneratedbyrollingcircles12.5RollingCirclesAreUsedtoReplicatePhageGenomes•TheφXAproteinisacis-actingrelaxasethatgeneratessingle-strandedcirclesfromthetailproducedbyrollingcirclereplication.FIGURE08:φX174RFDNAisatemplateforsynthesizingsingle-strandedviralcircles12.6TheFPlasmidIsTransferredbyConjugationbetweenBacteria•conjugation–Aprocessinwhichtwocellscomeincontactandtransfergeneticmaterial.–Inbacteria,DNAistransferredfromadonortoarecipientcell.•ThefreeFplasmidisarepliconthatismaintainedatthelevelofoneplasmidperbacterialchromosome.12.6TheFPlasmidIsTransferredbyConjugationbetweenBacteria•transferregion–AsegmentontheFplasmidthatisrequiredforbacterialconjugation.•AnFplasmidcanintegrateintothebacterialchromosome,inwhichcaseitsownreplicationsystemissuppressed.FIGURE09:ThetraregionoftheFplasmidcontainsthegenesneededforbacterialconjugation12.6TheFPlasmidIsTransferredbyConjugationbetweenBacteria•TheFplasmidcodesforaDNAtranslocationcomplexandspecificpilithatformonthesurfaceofthebacterium.•pilin–Thesubunitthatispolymerizedintothepilusinbacteria.•AnF-pilusenablesanF-positivebacteriumtocontactanF-negativebacteriumandtoinitiateconjugation.12.7ConjugationTransfersSingle-StrandedDNA•TransferofanFplasmidisinitiatedwhenrollingcirclereplicationbeginsatoriT.•Theformationofarelaxosomeinitiatestransferintotherecipientbacterium.•ThetransferredDNAisconvertedintodouble-strandedformintherecipientbacterium.12.7ConjugationTransfersSingle-StrandedDNA•WhenanFplasmidisfree,conjugation“infects”therecipientbacteriumwithacopyoftheFplasmid.FIGURE11:TransferofDNAoccurswhentheFplasmidisnickedatoriTandasinglestrandisledbythe5’endboundtoTraIintotherecipient12.7ConjugationTransfersSingle-StrandedDNA•WhenanFplasmidisintegrated,conjugationcausestransferofthebacterialchromosomeuntiltheprocessisinterruptedby(random)breakageofthecontactbetweendonorandrecipientbacteria.•Hfr–AbacteriumthathasanintegratedFplasmidwithinitschromosome.–Hfrstandsforhighfrequencyrecombination,referringtothefactthatchromosomalgenesaretransferredfromanHfrcelltoanF–cellmuchmorefrequentlythanfromanF+cell.12.7ConjugationTransfersSingle-StrandedDNAFIGURE12:TransferofchromosomalDNAoccurswhenanintegratedFplasmidisnickedatoriT12.8TheBacterialTiPlasmidCausesCrownGallDiseaseinPlants•Incrowngalldisease,infectionwiththebacteriumA.tumefacienscantransformplantcellsintotumors.•TheinfectiousagentistheTiplasmidcarriedbythebacterium.•Theplasmidalsocarriesgenesforsynthesizingandmetabolizingopines(argininederivatives)thatareusedbythebacterium.12.8TheBacterialTiPlasmidCausesCrownGallDiseaseinPlants•nopalineplasmids–TiplasmidsofAgrobacteriumtumefaciensthatcarrygenesforsynthesizingtheopine,nopaline.–Theyretaintheabilitytodifferentiateintoearlyembryonicstructures.•octopineplasmids–PlasmidsofAgrobacteriumtumefaciensthatcarrygenescodingthesynthesisofopinesoftheoctopinetype.–Thetumorsareundifferentiated.12.8TheBacterialTiPlasmidCausesCrownGallDiseaseinPlants•agropineplasmids–Plasmidsthatcarrygenescodingforthesynthesisofopinesoftheagropinetype.–Thetumorsusuallydieearly.•Riplasmid–PlasmidsfoundinAgrobacteriumtumefaciens.LikeTiplasmids,theycarrygenesthatcausediseaseininfectedplants.–Thediseasemaytaketheformofeitherhairyrootdiseaseorcrowngalldisease.12.9T-DNACarriesGenesRequiredforInfection•T-DNA,partoftheDNAoftheTiplasmid,istransferredtotheplantcellnucleus.FIGURE15:T-DNAistransferredfromAgrobacteriumcarryingaTiplasmidintoaplantcell12.9T-DNACarriesGenesRequiredforInfection•ThevirgenesoftheTiplasmidarelocatedoutsidethetransferredregionandarerequiredforthetransferprocess.•Thevirgenesareinducedbyphenoliccompoundsreleasedbyplantsinresponsetowo