遗传及基因重组的分子机制.ppt

2.真核生物中的转座成分Ty因子Ds-Ac系统P、FB、copia反转录转座子(1)Ty转座元件靶位两侧形成5bpDR以RNA为中介(2)Ds-Ac系统CS9发生断裂的原因Ds基因的作用?CS断裂的机率提高?转座,抑制功能基因表达Ds的转座Ds-Ac体系作用模式有色色斑无色无色凹陷Ds-Ac的组成及作用特点Ds:非自主元件,0.5?4.0kb,与Ac有同源序列Ac:自主元件,4.5kb,5个exon,编码转座酶,IR5?-CAGGGATGAAA…TTTCATCCCTG-3?3?-GTCCCTACTTT…AAAGTAGGGAC-5?(3)果蝇的转座因子P因子Copia因子FB因子CompletePelement?allsequencespresentIncompletePelements?internalsequencesmissingM♀蝇?P♂蝇?不育M♂蝇?P♀蝇?可育P型:P因子,30?50拷贝M型:无P因子P-Mhybriddysgenesis果蝇P因子不育机理ORFORF0…ORF1…ORF2…ORF3内含子123P因子表达差异：体细胞ORF0,1,2?66kD,转座阻遏物性细胞ORF0,1,2,3?87kD,转座酶Germ-line-specificexpressionofDrosophilaPelements:anexampleoftissue-specificregulationbyRNAsplicing(a)Thesomaticandgerm-linemRNAstructuresforawild-typePelementareshown.Thegerm-linemRNAisformedbysplicingoffourexons(No.0to3)andencodesPtransposase.ThesomaticmRNAlacksthesplicebetweenE2andE3;thatis,theintronbetweenthesetwoexonsisretainedinthemRNA.BecausetheintronbetweenE2andE3containsastopcodon,theresultingshortersomaticproteinisdefective,lackingthetransposaseactivity.(b)AmodifiedPelementtransgene,P(△2,3),thatlackstheintronbetweenE2andE3isdepicted.Inalltissues,P(△2,3),producesanmRNAindistinguishablefromthatofthewild-typePelement,resultinginPtransposaseactivityinbothgermlineandsoma.P或M♂?P♀(转座阻遏物)↓P因子不转座,可育P♂?M♀(不含阻遏物)↓P因子转座,不育E.coli四种重组的一般特征类型是否需要是否需要是否需要序序列同源性RecA蛋白列特异性酶同源重组是是否位点特异是否是异常重组否否?转座作用否否是12.2同源重组的分子机制异源双链断裂与重接Hollidaymodelgeneconversion同源重组的基本条件交换区为相同或相似序列两dsDNA分子间互补重组酶参与异源