11第11章转座子和逆转座子

3. 非复合型转座子 Noncomposite transposons
反向重 复序列
转座酶
抑制酶 氨苄青霉 素抗性
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共整合体
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第二节 真核生物的转座因子
Transposable Elements in Eukaryotes

DNA 转座子 (cut and paste transposons)
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病毒与真核生物基因组中逆转座子结构比较
鼠白血病毒
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酵母TY系列（Yeast Ty elements）
About 35 Ty1 copies in the yeast genome.
δ sequences : 330 bp, about 100 copies. solo δ element.

An IS element ends in short inverted terminal repeats ; usually the two copies of the repeat are closely related rather than identical. IS elements code for the transposase. When an IS element transposes, a sequence of host DNA at the site of insertion is duplicated.
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反向重 复序列
体细胞
终止密码子 阻遏蛋白
生殖细胞
转座酶 32
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）
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P-elementmediated gene transfer in
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转座因子的发现
Discovery of Transposable Elements

McClintock’s experiments in maize: the Ds element
1940-1950
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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 ): located at the site of the break 激活因子 ( Activator,Ac ) : unlinked genetic factor
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37 ※ ※The life cycle of a retrovirus
病毒侧翼序列
The typical genome of a retrovirus contains gag, pol, and env genes
菱形衣 壳蛋白
外壳蛋白 逆转录酶
逆转录病毒 38 基因表达

逆转录病毒可随机整合到宿主细胞。
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。
A DNA sequence capable of moving ( transposing) from one location to another in a genome.
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启动子 增强子
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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。 （Transposable elements that utilize reverse transcriptase to transpose through an RNA intermediate are termed retrotransposons. ） 退化的逆病毒
第11章 转座子和逆转座子
Transposons and retrotansposons
The 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.
A schematic map of a plasmid carrying simple and composite transposon-resistance genes.
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• IS序列既可以自我转座又可以和复合转座 子共同转座。
A functional IS module can transpose either itself or the entire transposon.
Drosophila
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3. 反转录病毒与反转座子 Retroviruses and Retroposons
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。 Retroviruses are single-stranded RNA animal viruses that employ a double-stranded DNA intermediate for replication.

Ac and Ds elements in maize
P elements in Drosophila

反转座子 （Retrotransposons）
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1.玉米的Ac-Ds 转座系统 （The Ac-Ds system in maize）
Barbara McClintock (1902-1992) 1940s ~ 1950s 1983 Nobel Prize
ቤተ መጻሕፍቲ ባይዱ15
Formation of a conjugative R plasmid by recombination between IS elements
(Resistance transfer factore,RTF)
细菌耐药性
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2. 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.

Simple transposable elements which carry only the information required for movement.

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）。

Complex transposable elements which contain DNA sequences not directly related to transposition.
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Movie
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玉米中转座因子效应
？
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其它植物中的转座因子
Transposable element in other plants
直链
SBE
支链 peas snapdragons
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2. 果蝇的P因子
P element transposons in Drosophilia 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.
• 当IS序列完全相同时，两者均可独立进行 转座。
When the two IS modules are identical, either module can sponsor the transposition.
• 当IS序列不完全相同时，两者之一引发转 座，L。
When the modules are different, transposition can depend on one of the modules
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1.插入序列 (Insertion sequences，IS)
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。
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插入序列的结构 The structure of IS element
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正向重复序列
反向重复序列
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插入序列特点：

插入序列末端两重复序列高度相似但不完全相同。
四环素
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氯霉素
卡拉霉素 四环素 18
复合转座子特点：

一些复合转座子两端的IS序列完全相同的， 如Tn9和Tn903。

In some cases, IS modules are identical, such as Tn9 (direct repeats of IS1) or Tn903 (inverted repeats of IS903).
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插入序列的中间序列常具有编码转座酶的功能。


插入序列转座后常导致靶位点的重复。

Duplication of a short sequence of DNA at the insertion site
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The IS elements are normal constituents of bacterial chromosomes and plasmids.