交大微生物课件genetics

HowcanabacteriumchangeitselfbytakinggenesfromotherLectureLecture10-2BacterialII.ExchangeofgeneticinformationbetweenbacterialcellsChapter10BROCKBIOLOGYOFSchoolofLifeScienceandTechnology,ShanghaiJiaoTongUniversityShanghaiJiaoTong bination遗传重ThephysicalexchangeofgeneticmaterialbetweengeneticelementsGeneticShanghaiJiaoTongMolecularEventsinHomologousbination同源重组Generalor binationGeneticexchangebetweenhomologousDNAsequencesfromtwodifferentsourcesHomologousDNAsequencesHavingthesameornearlythesamesequenceExtremelyimportantforallorganisms重要性25genesinvolvedinE.coliSeveralredundantpathways.Thereforeifonepathwayisinhibited,anothermaysupplynecessaryfunctions.有数条替代途径备用Molecularmechanismof NickStrandResolutionofheteroduplex(SSB)single-strandedbindingShanghaiJiaoTongProcessesleadingtogenetic binationinprokaryoticcells原核生物遗传重组的类型TransformationDonorDNA intheTransductionDonorDNAistransferredbyConjugationDonorDNAistransferredviacell-to-cellcontactanda Figure:10-TransformationDonorDNA intheTransductionDonorDNAistransferredbyConjugationDonorDNAistransferredviacell-to-cellcontactanda ShanghaiJiaoTongTransformationTransformationisaprocessbywhich DNAisincorporatedintoarecipientcellandbringsaboutgeneticchange.转化是游离DNA进ShanghaiJiaoTong MechanismoftransformationBindingdsDNAbyamembrane-boundDNAbindingprotein.Passage单链结合蛋

oneofthetwostrandsintothecellwhiledegradestheotherstrand.Thesinglestrandinthecellisboundbyspecificproteins,andbinationwithhomologousregionsofthebacterialchromosomemediatedbyRecAproteinoccurs.(d)(d)Transformedcell.Ifbinationdoesnotoccur,cannotreplicateandwillbelost.ingShanghaiJiaoTongTransduction

TwokindsofGeneralizedtransduction:DNAfromanyportionofthehost esapartofthematurevirionin ceofthegenome.普遍性转导Specializedtransduction:DNAfromspecificregionofthehostchromosomeisintegratedDNA

Figanyportionthehostgenome apartofthematurevirionin ceoftheFigFigDNAfromaspecificregionofthehostchromosomeisintegrateddirectlyintogenome-usuallyre someofthe ShanghaiJiaoTongsmidandsmidsaregeneticelementsthatreplicateindependentlyofthehostchromosome.Conjugationismediatedbyconjugative Conjugationiscontrolledbyasetofgeneswithinthesmidcalledthetra(fortransferregion接合质粒的 Example: Structureof oriTsequenceistheoriginoftransferduringconjugation.Thearrowindicatesthedirectionoftransfer(thetraregionwouldbetransferred

Figure:10-traregionthegenesinvolvedinconjugativetransfer. genesprimarilyresponsibleforreplicationandsegregationoftheFsmidin growingShanghaiJiaoTongConjugation:EssentialCell-to-CellTransfer smidsduringConjugationConjugationbetweendifferentFigDirectcontactbetweentwoconjugatingbacteriaisfirstmadeviaapilus.ThecellsarethendrawntogethertoformamatingpairfortheactualtransferofDNA.靠近形成杂交对供体DNAShanghaiJiaoTongMechanismofDNAtransferDuringAmechanismofDNAsynthesisincertainbacteriophages,calledrollingcirclereplication,bestex insDNAtransferduringconjugation.可用滚环 ReviewofMechanismofconjugativetransfer smidFig.10.22TheFsmidofanF+cellisbeingtransferredtoanF-recipientcell.Notethemechanismofrollingcirclereplication.F质粒通过滚环转移到Conjugationistriggeredbycell-to-cellcontact,atwhichtimeonestrandofthesmidDNAcircleisnickedandistransferredtotherecipient.Asthistransferoccurs,DNAsynthesisbytherollingcirclemechanism cesthetransferredstrandinthedonor,whilethecomplementaryDNAstrandismadeintheFig.10.22bFig.10.22bDetailsofthereplicationandtransferprocess.ShanghaiJiaoTongTheFormationofHfrStrainsandChromosomeMobilizationp.279SectionUndercertaincircumstances,F smidofE.colicanmobilizethechromosomefortransferduringcell-to-cell ShanghaiJiaoTongF+andHfrF+:CellspossessinganunintegratedFsmidHfr:Cellsthathaveachromosome-integratedsmid.(highfrequencyof BothF+andHfrcellsaredonorsandareunabletotakeupasecondcopyofthesmidorgenetically 10.11.1IntegrationofF smidandChromosome IntegrationofF smidintohostchromosomecanoccuratIS(forinsertionOnceintegrated, smidnolongercontrolsitsownreplication,butthetraoperonstillfunctionsnormallyandthestrainsynthesizespili.Figure:10-BreakageoftheHfrchromosomeattheoriginoftransferandthebeginningofDNAtransfertotherecipientWhenarecipientisencountered,DNAtransferisinitiatedattheoriTsite.

Afterpartofthe DNAistransferred,chromosomalgenesbegintobetransferred.BreakageoftheHfrchromosomeattheoriginoftransferandthebeginningofDNAtransfertotherecipientAftertransfer,theHfrstrainremainsgeneticallyHfrbecauseitretainsacopyofthetransferredgenes.Hfr菌株在

Breakagetypicallyoccursduringtransfer,onlypartofthedonorchromosomeis ShanghaiJiaoTong10.11.2UseofHfrStrainsShanghaiJiaoTongDetectionofarecipientthatisresistanttoanantibioticbutisauxotrophic(strr/lac-).受体对抗生素有抗性但为营养缺陷型Adonorthatissensitivetotheantibioticbutisprototrophicforthesamesubstance(strs/lac+).供体对抗生素敏感但为Thus,onminimalmediumcontainingtheantibiotic,onlyrecipientcellswillgrowfollowingthematingevent在含抗生ShanghaiJiaoTongFigFig10.26LaboratoryprocedurefordetectionofgeneticShanghaiShanghaiJiaoTongInterruptedmatingandgeneticmap中断杂交方法与遗传图谱绘Interruptedmating:Conjugatingcellscan it Genespresentclosertothe it

entertheF-ThisExperimentprovideamethodofdeterminingtheThisExperimentprovideamethodofdeterminingtheorderofthege