转座子,转座机制

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1、BacterialTransposons•Atransposableelement转座因子movesfromoneDNAaddresstoanother•Originallydiscoveredinmaize,transposonshavebeenfoundinallkindsoforganisms–Bacteria–Plants–HumansDiscoveryofBacterialTransposons•Phagecoatismadeofprotein•Alwayshasthesamevolume同体积•DNAismuchdenserthanproteinDNA密度大•MoreDNAinp

2、hage,denserphage若DNA含量高，其密度就大•ExtraDNAsthatcaninactivateagenebyinsertingintoitwerethefirsttransposonsdiscoveredinbacteria发现gal基因的失活是因为插入了一段野生型基因中没有的DNA，这就是转座子•Thesetransposonsarecalledinsertionsequences(ISs)插入序列InsertionSequences•InsertionsequencesarethesimplesttypeofbacterialtransposonIS是最简单的细菌转座子

3、•Theycontainonlytheelementsnecessaryfortheirowntransposition仅包含满足自身转座需要的因子：–Shortinvertedrepeatsattheirends末端短的反向重复序列–Atleast2genescodingforanenzyme,transposasethatcarriesouttransposition由至少两个基因编码的转座酶•Transpositioninvolves:–DuplicationofashortsequenceinthetargetDNA复制靶DNA的一段短序列–Onecopyofthissequence

4、flankstheinsertionsequenceoneachsideaftertransposition转座后插入序列侧翼各有一个拷贝GeneratingHostDNADirectRepeatsComplexTransposons•Theterm“selfishDNA”impliesthatinsertionsequencesandothertransposonsreplicateattheexpenseoftheirhosts,providingnovalueinreturn插入序列或者其它转座子是自私的•Sometransposonsdocarrygenesthatarevaluab

5、letotheirhosts,antibioticresistanceisamongmostfamiliar但有的转座子可以为宿主提供有益的东西，如抗生素抗性基因AntibioticResistanceandTransposonsTranspositionMechanisms•Transposonsaresometimescalled“jumpinggenes”,DNAdoesn’talwaysleaveoneplaceforanother转座子也被叫作跳跃基因（但有误导）•Whenitdoes,nonreplicativetransposition非复制式转座–“Cutandpaste”–

6、BothstrandsoforiginalDNAmovetogetherfrom1placetoanotherwithoutreplicating•TranspositionfrequentlyinvolvesDNAreplication–1copyremainsatoriginalsite–Newcopyinsertsatthenewsite–Replicativetransposition复制式转座–“Copyandpaste”ReplicativeTranspositionofTn323-11DetailedTn3TranspositionNonreplicativeTransposi

7、tionEukaryoticTransposons•Transposonshavepowerfulselectiveforcesontheirside转座子会赋予寄主强大的选择压•Transposonscarrygenesthatareanadvantagetotheirhosts转座子携带有利的基因–Theirhostcanmultiplyattheexpenseofcompletingorganisms因