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1、第第11章章 转座子和逆转座子转座子和逆转座子Transposons and retrotansposonsThe sun1642 tomato variety produces an elongated fruit,which is produced by a duplication that arose as a result of the presence of the transposable element Rider.转座子转座子 ( transposon,Tn) n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。 A DNA sequence capab
2、le of moving ( transposing) from one location to another in a genome. 2Discovery of Transposable ElementsnMcClintocks experiments in maize: the Ds element 1940-19503转座因子的发现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。对染色体。解离因子解离因子 ( Dissociation,Ds ): located at the site of the break激活因子激
3、活因子 ( Activator,Ac ) : unlinked genetic factor45n Transposable element in E. coli , 19606转座子的分类转座子的分类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第一节 细菌的转座因子细菌的转座因子 Transposable elements in Bacteria 两大类两大类: n简单转座因子：简单转座因子：只包含和转座有关的基因序列。只包含和转座有关的基因序列。 Simple transposable elements which carry only the informa
4、tion required for movement.n复合转座因子：复合转座因子：除了含有与转座相关的基因外还有其它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）。基因（如抗生素抗性基因）。Complex transposable elements which contain DNA sequences not directly related to transposition.81.插入序列插入序列 (Insertion sequences，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。插入序列的结构插入序列的结构The structure of IS
5、element1011正向重复序列反向重复序列12n插入序列末端两重复序列高度相似但不完全相同。插入序列末端两重复序列高度相似但不完全相同。An IS element ends in short inverted terminal repeats ; usually the two copies of the repeat are closely related rather than identical. n插入序列的中间序列常具有编码转座酶的功能。插入序列的中间序列常具有编码转座酶的功能。IS elements code for the transposase.n插入序列转座后常导致插入序
6、列转座后常导致靶位点的重复靶位点的重复。When an IS element transposes, a sequence of host DNA at the site of insertion is duplicated.13插入序列特点：插入序列特点：Duplication of a short sequence of DNA at the insertion site14The IS elements are normal constituents of bacterial chromosomes and plasmids. 15Formation of a conjugative R
7、 plasmid by recombination between IS elements16(Resistance transfer factore,RTF)细菌耐药性2. 复合转座子复合转座子Composite Transposons Composite transposons contain a variety of genes that reside between two nearly identical IS elements .Composite transposon is designated by Tn, followed by a number.17四环素18氯霉素四环素卡
8、拉霉素n一些复合转座子两端的一些复合转座子两端的IS序列完全相同的，序列完全相同的，如如Tn9和和Tn903。In some cases, IS modules are identical, such as Tn9 (direct repeats of IS1) or Tn903 (inverted repeats of IS903). n另外一些转座子中，另外一些转座子中，IS非常相似但不完全非常相似但不完全相同，因而用相同，因而用R和和L表示。表示。In other cases, the modules are closely related, but not identical. So
9、we can distinguish the L and R modules in Tn10 or in Tn5. 复合转座子特点：复合转座子特点：A schematic map of a plasmid carrying simple andcomposite transposon-resistance genes.20IS序列既可以自我转座又可以和复合转座序列既可以自我转座又可以和复合转座子共同转座。子共同转座。A functional IS module can transpose either itself or the entire transposon. 当当IS序列完全相同时，两
10、者均可独立进行序列完全相同时，两者均可独立进行转座。转座。When the two IS modules are identical, either module can sponsor the transposition.当当IS序列不完全相同时，两者之一引发转序列不完全相同时，两者之一引发转座，座，L。When the modules are different, transposition can depend on one of the modules3. 非复合型转座子非复合型转座子Noncomposite transposons22转座酶抑制酶氨苄青霉素抗性反向重复序列23共整合体
11、第二节第二节 真核生物的转座因子真核生物的转座因子Transposable Elements in EukaryotesnDNA 转座子 (cut and paste transposons)nAc and Ds elements in maizenP elements in Drosophilan反转座子 （Retrotransposons）24 1.玉米的玉米的Ac-Ds 转座系统转座系统 （The Ac-Ds system in maize）Barbara McClintock (1902-1992)1940s 1950s1983 Nobel Prize2526Movie玉米中转座因子效
12、应玉米中转座因子效应27？28其它植物中的转座因子其它植物中的转座因子Transposable element in other plantspeassnapdragons29SBE直链直链 支链支链 杂交劣育（Hybrid dysgenesis）: a condition causing sterility, elevated mutation rate, and a chromosome rearrangement in the offspring of crosses between certain strains of fruit flies. 302. 果蝇的果蝇的P因子因子 P e
13、lement transposons in Drosophilia3132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。（The 66KD repressor protein is provided as a maternal factor in the egg）33P-element-mediated genetransfer in Drosophila343. 反转录病毒与反转座子反转录病毒与反转座子 Retroviruses and Retroposons 反转录病毒：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
14、染。Retroviruses are single-stranded RNA animal viruses that employ a double-stranded DNA intermediate for replication. 3536The life cycle of a retrovirus37The typical genome of a retrovirus contains gag, pol, and env genes逆转录病毒逆转录病毒基因表达基因表达38菱形衣壳蛋白外壳蛋白逆转录酶病毒侧翼序列n逆转录病毒可随机整合到宿主细胞。The viral DNA integrat
15、es into the host genome at randomly selected sites. n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 (probably rather rarely), the integrated retrovirus can convert a host cell into a tumorigenic state through activating certain types of host genes.3940启动子增强子 逆转座子逆转座子（Retroposon） 逆转录转座子指通过逆转录转座子指通过RNA为中介为中介,反
16、转录成反转录成DNA后进行转座的转座因子。逆转座作用出现在后进行转座的转座因子。逆转座作用出现在真核生物。真核生物。 （Transposable elements that utilize reverse transcriptase to transpose through an RNA intermediate are termed retrotransposons. ）退化的逆病毒42 逆转座子在真核生物中可分为两类：逆转座子在真核生物中可分为两类：病毒样逆转座子病毒样逆转座子 (Viral retrotransposons): 与反转录病毒结构类似，不同之处在于不形成病毒颗粒。 如Yea
17、st Ty elements, Drosophila copia elements非病毒样逆转座子非病毒样逆转座子 (Nonviral retrotransposons ) : 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 (long interspersed elements) and SINEs in mammals43病毒与真核生物基因组中逆转座子结构比较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n酵母TY系列（Yeast Ty elements） About 35 Ty1 copies in the yeast genome. se
18、quences : 330 bp, about 100 copies. solo element.45*3.Base substitution for marking one Transposition through an RNA intermediate462.半乳糖诱导启动子半乳糖诱导启动子1实验证明：实验证明：nDrosophila copia elements 47转座因子的频率转座因子的频率n不同的转座因子的转座频率不同。n每个世代转座频率约为10-3 10-4 。nNew germ-line transpositions are estimated to occur once i
19、n every 50 to 100 human births.n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第三节第三节 转座的遗传学效应转座的遗传学效应 Genetic effect of transposition49Transposable elements as genetic parasitesReplication and spread of Tes may serve no purpose for the cell.The insertion of Tes into a gene will often destroy its f
20、unction, with harmful consequences for the cell.The time and energy require to replicate large numbers of Tes are likely to place a metabolic burden on the cell.人类中的转座子人类中的转座子50Repetitive elements found in the human gene (HGO) coding for homogentisate 1,2-dioxygenase(尿黑酸尿黑酸-1,2-氧氧化酶化酶), the enzyme w
21、hose deficiency causes alkaptonuria（尿黑酸尿）（尿黑酸尿）.The Alu sequences make up more than 10% of the human genome.51Transposable elements in grasses are responsible for genome size differences其它生物中的转座因子其它生物中的转座因子Green: transposons; Orange: genes52转座因子引起的遗传效应转座因子引起的遗传效应 基因突变（编码区）基因突变（编码区） 染色体结构改变（非编码区）染色体结
22、构改变（非编码区）Transposoble element can generate mutations in adjacent genesAbout 50% of all spontaneous mutations in Drosophila are due to transposition, 10%(mouse), 0.2%(human).54Retrotransposon-InducedMutations in Grape Skin ColorSCIENCE, 14 MAY 2004, VOL 30455Transposable elements can cause rearrangem
23、ents of the genomedeletioninversion56Relocate genes57Evolutionary Significance of Transposable Elementsn转座子的驯化转座子的驯化nTransposase(转座酶) regulate plant genes in ArabidopsisnTelomerase and reverse transcriptase （果蝇） 58nHow do plants and animals survive and thrive with so many insertions in genes and so much mobile DNA in the genome?n安全岛（safe heavens）n多拷贝基因（基因组较小的生物）n宿主细胞表观遗传调控宿主与转座因子在细胞内处于不断博弈过程中。59思考题：思考题：1、结合所学的知识，试分析一些致病菌、结合所学的知识，试分析一些致病菌极易产生抗药性的原因？极易产生抗药性的原因？2、试分析生物是如何避免基因组中转座、试分析生物是如何避免基因组中转座行为所引起有害突变的。行为所引起有害突变的。
