11第11章转座子和逆转座子

第11章转座子和逆转座子TransposonsandretrotansposonsThesun1642tomatovarietyproducesanelongatedfruit,whichisproducedbyaduplicationthataroseasaresultofthepresenceofthetransposableelementRider.转座子(transposon,Tn)基因组中可以从一个基因座转移到另一个基因座，具有移动能力的一段DNA片段。ADNAsequencecapableofmoving(transposing)fromonelocationtoanotherinagenome.2DiscoveryofTransposableElementsMcClintock’sexperimentsinmaize:theDselement1940-19503转座因子的发现印第安彩虹玉米，具有从最大到最小易于区分的10对染色体。解离因子(Dissociation,Ds):locatedatthesiteofthebreak激活因子(Activator,Ac):unlinkedgeneticfactor45TransposableelementinE.coli,19606转座子的分类7非复制性的转座（占已经发现的多数）复制性逆转座逆转座病毒样的转座子第一节细菌的转座因子TransposableelementsinBacteria两大类:简单转座因子：只包含和转座有关的基因序列。Simpletransposableelementswhichcarryonlytheinformationrequiredformovement.复合转座因子：除了含有与转座相关的基因外还有其它基因（如抗生素抗性基因）。ComplextransposableelementswhichcontainDNAsequencesnotdirectlyrelatedtotransposition.81.插入序列(Insertionsequences，IS)9不含任何宿主基因的可转位的DNA序列，是最简单的转座因子。插入序列的结构ThestructureofISelement1011正向重复序列反向重复序列12插入序列末端两重复序列高度相似但不完全相同。AnISelementendsinshortinvertedterminalrepeats;usuallythetwocopiesoftherepeatarecloselyrelatedratherthanidentical.插入序列的中间序列常具有编码转座酶的功能。ISelementscodeforthetransposase.插入序列转座后常导致靶位点的重复。WhenanISelementtransposes,asequenceofhostDNAatthesiteofinsertionisduplicated.13插入序列特点：DuplicationofashortsequenceofDNAattheinsertionsite14TheISelementsarenormalconstituentsofbacterialchromosomesandplasmids.15FormationofaconjugativeRplasmidbyrecombinationbetweenISelements16(Resistancetransferfactore,RTF)细菌耐药性2.复合转座子CompositeTransposonsCompositetransposonscontainavarietyofgenesthatresidebetweentwonearlyidenticalISelements.CompositetransposonisdesignatedbyTn,followedbyanumber.17四环素18氯霉素四环素卡拉霉素一些复合转座子两端的IS序列完全相同的，如Tn9和Tn903。Insomecases,ISmodulesareidentical,suchasTn9(directrepeatsofIS1)orTn903(invertedrepeatsofIS903).另外一些转座子中，IS非常相似但不完全相同，因而用R和L表示。Inothercases,themodulesarecloselyrelated,butnotidentical.SowecandistinguishtheLandRmodulesinTn10orinTn5.复合转座子特点：Aschematicmapofaplasmidcarryingsimpleandcompositetransposon-resistancegenes.20•IS序列既可以自我转座又可以和复合转座子共同转座。AfunctionalISmodulecantransposeeitheritselfortheentiretransposon.•当IS序列完全相同时，两者均可独立进行转座。WhenthetwoISmodulesareidentical,eithermodulecansponsorthetransposition.•当IS序列不完全相同时，两者之一引发转座，L。Whenthemodulesaredifferent,transpositioncandependononeofthemodules3.非复合型转座子Noncompositetransposons22转座酶抑制酶氨苄青霉素抗性反向重复序列23共整合体第二节真核生物的转座因子TransposableElementsinEukaryotesDNA转座子(cutandpastetransposons)AcandDselementsinmaizePelementsinDrosophila反转座子（Retrotransposons）241.玉米的Ac-Ds转座系统（TheAc-Dssysteminmaize）BarbaraMcClintock(1902-1992)1940s~1950s1983NobelPrize2526Movie玉米中转座因子效应27？28其它植物中的转座因子Transposableelementinotherplantspeassnapdragons29SBE直链支链杂交劣育（Hybriddysgenesis）:aconditioncausingsterility,elevatedmutationrate,andachromosomerearrangementintheoffspringofcrossesbetweencertainstrainsoffruitflies.302.果蝇的P因子PelementtransposonsinDrosophilia3132反向重复序列体细胞生殖细胞终止密码子阻遏蛋白转座酶66KD的转座阻遏蛋白是造成现象差异的主要原因。（The66KDrepressorproteinisprovidedasamaternalfactorintheegg）33P-element-mediatedgenetransferinDrosophila343.反转录病毒与反转座子RetrovirusesandRetroposons反转录病毒：单链的RNA病毒，依靠独立的双链DNA中间体结构进行感染。Retrovirusesaresingle-strandedRNAanimalvirusesthatemployadouble-strandedDNAintermediateforreplication.3536※Thelifecycleofaretrovirus※37Thetypicalgenomeofaretroviruscontainsgag,pol,andenvgenes逆转录病毒基因表达38菱形衣壳蛋白外壳蛋白逆转录酶病毒侧翼序列逆转录病毒可随机整合到宿主细胞。TheviralDNAintegratesintothehostgenomeatrandomlyselectedsites.有时（几率较小）逆转录病毒可能将宿主细胞转化为肿瘤细胞。Sometimes(probablyratherrarely),theintegratedretroviruscanconvertahostcellintoatumorigenicstatethroughactivatingcertaintypesofhostgenes.3940启动子增强子逆转座子（Retroposon）逆转录转座子指通过RNA为中介,反转录成DNA后进行转座的转座因子。逆转座作用出现在真核生物。（TransposableelementsthatutilizereversetranscriptasetotransposethroughanRNAintermediatearetermedretrotransposons.）退化的逆病毒42逆转座子在真核生物中可分为两类：◇病毒样逆转座子(Viralretrotransposons):与反转录病毒结构类似，不同之处在于不形成病毒颗粒。如YeastTyelements,Drosophilacopiaelements◇非病毒样逆转座子(Nonviralretrotransposons):不形成逆转录酶和整合酶，依靠外源提供的转座酶，真核生物基因组中所占比例最高。LINEs(longinterspersedelements)andSINEsinmammals43病毒与真核生物基因组中逆转座子结构比较44鼠白血病毒酵母TY系列（YeastTyelements）About35Ty1copiesintheyeastgenome.δsequences:330bp,about100copies.soloδelement.45**3.BasesubstitutionformarkingoneδTranspositionthroughanRNAintermediate462.半乳糖诱导启动子1实验证明：Drosophilacopiaelements47转座因子的频率不同的转座因子的转座频率不同。每个世代转座频率约为10-3~10-4。Newgerm-linetranspositionsareestimatedtooccuronceinevery50to100humanbirths.每个世代中转座插入靶位点使某个基因所引起的突变和自发突变概率相当，约为10-5~10-7。48第三节转座的遗传学效应Geneticeffectoftransposition49TransposableelementsasgeneticparasitesReplicationandspreadofTesmayservenopurposeforthecell.TheinsertionofTesintoagenewilloftendestroyitsfunction,withharmfulconsequencesforthecell.ThetimeandenergyrequiretoreplicatelargenumbersofTesarelikelytoplaceametabolicburdenonthecell.人类中的转座子ElementtypeLengthCopiesingenome%ofgenomeLINEs1-6kb850,00021SINEs100-500bp1,500,00013%LTRelements5kb443,0008DNAelements80-300bp294,0003Unclassified-3,0000.1%50Repetitiveelementsfoundinthehumangene(HGO)codingforhomogentisate1,2-dioxygenase(尿黑酸-1,2-