谈谈转座因子

传统的基因概念认为基因在染色体上是一个稳定的实体,它是不会改变其功能的,除非发生基因突变。而且基因不会任意移动位置和插入到其它染色体中去。但是近年的研究表明,有些遗传因子或基因不仅能改变功能,而且可以任意移动而改变原来的位置。这种可移动的基因或核苷酸顺序被切下后可整合到其它染色体上,这种移动现象称转座。这种可转移位置的因子称转座因子(transposable ele-ments)也称跳跃基因(jumping gene)。早在1932年,麦克林托克(Mc Clintock)     

谈谈改变传统观念的转座因子

在五十年代前,人们一直认为每一基因组的 DNA是固定的,包括位置固定、数目固定。转座因子的发现修正了这一观念。现在人们认识到基因组中的某些成分的位置常常是不固定的,一种生物的基因组大小或基因的数目也并非绝对不变。这种位置不固定的成分乃是转座因子。转座因子(transpos-able element)是细胞中能够改变自身位置的一段 DNA 序列。转座因子改变位置的行为称转座(transposition),转座可以发生在同一染色体的不同位置之间,不同的     

杆状病毒转座因子研究进展

转座因子(Transposable elements)是一类可移动转座的遗传因子的统称,包括原核生物中的插入(IS)、转座子(Tn)、质粒;真核生物中的Ty,P因子,2μDNA,Copia因子,以及噬菌体Mu和反转录病毒等。因此,转座因子又称可移动的遗传因子(Mobile genetic element)。转座因子最早由美国科学家Barbara McClintock于1956年在玉米染色体中发现,并于1984年被授予诺贝尔医学或生理学奖。转座因子的发现无论在理论上还是实践上都具有很重要的意义,被认为是遗传学发展史上的重要里程碑之一。杆状病毒是一类以节肢动物(主要发现于昆虫纲鳞翅目)为宿主的病毒的统称。杆状病毒亦存在转座因子。对杆状病毒转座因子的研究起源于对感     

转座因子标签法

转座因子(Transposable element)是Mc-Clintock在玉米的染色体上首先发现的,以后在大肠杆菌、酵母、果蝇、线虫、蚕及金鱼草与矮牵牛等植物中也陆续发现了转座因子的存在。转座因子的发现是遗传学发展史上的重要里程碑,是本世纪遗传学领域内重大的发现之一,在理论和实际应用上都有重要的意义。近年来,由于分子遗传学研究的进步,对转座因子的结构、转座的机理等方面的研究取得了很大的成绩,转座因子的应用研究开始受到人们的重视,特别在应用转座因子作为标签来分离高等植物基因的研究中取得了令人瞩目的成绩。本文就转座因子标签法分离高等植物基因的研究进展作一大致的介绍。     

可转座基因与植物基因组多样性

高等植物基因组含有大量各式各样的串联重复序列和出现频率很高的散布重复序列,如转座子、反转座子、短散布核元件和一些新发现的小型转座子等,它们当中的大多数是具有移动能力的可转座基因.这些可转座基因在漫长的进化过程中对基因和基因组多样性的形成所起的作用,成为近年来分子生物学领域中的重要研究内容.     

异源植物中转座因子标签研究的进展

异源植物中转座因子标签研究的进展瞿绍洪１,２）景健康１）胡含１）（１中国科学院遗传研究所,北京１００１０１;２中国科学院植物研究所,北京１０００９３）ＰｒｏｇｒｅｓｏｆＴｒａｎｓｐｏｓｏｎＴａｇｇｉｎｇｉｎＨｅｔｅｒｏｌｏｇｏｕｓＰｌａｎｔｓＱｕＳｈ...     

果蝇转座因子对基因组进化的影响

真核生物基因组织有很多可移动ＤＮＡ片段为称转座因子,果蝇是大量系统研究的最好实验材料之一,其基因组的１０％－１２％是由转座因子组成,在宿主中,ＴＥs也许改变基因表达模型,也许改变ＯＲＦs编码序列,也许对细胞功能产生影响,这此因子遗传的可动性也可能使它们适于建造载体产生转基因生物。因此,对ＴＥs进化的动态研究以及对宿主基因组进化影响的探索将有助于TEs作为载体的细胞工程研究。     

哺乳动物PB转座因子研究

人类基因组计划发现哺乳动物体内存在大约30000个基因,将遗传蓝图的“天书”展示在人们面前。我国科研人员为此贡献了1％的测序结果。目前,国际竞争的焦点已经转向如何迅速了解这些基因的功能,从中找出有重大理论意义及经济效益的基因,即功能基因组研究。哺乳动物基因功能研究不仅有助于人类认识自我,具有重要的理论意义,而且疾病相关基因的研究也对发展针对性的预防、诊断和治疗手段具有决定性作用,因而成为世界生物科技产业竞争的焦点。     

链霉菌的可转座因子

可转座因子是细菌遗传分析和分子操作十分有用的工具 ,它包括插入序列、转座子和转座噬菌体。细菌的可转座因子多数来自于革兰氏阴性菌 ,少数来自于革兰氏阳性菌。链霉菌是一类重要的革兰氏阳性菌 ,近年来 ,已发现了几种链霉菌的可转座因子 ,并对部分可转座因子的转座特征作了详细的研究。最早发现的链霉菌可转座因子是天蓝色链霉菌 (Ｓ .ｃｏｅｌｉｃｏｌｏｒ)Ａ3( 2 )中 1 6ｋｂ的插入片断ＩＳ1 1 0 [1 ] ,后来在白色链霉菌 (Ｓ .ａｌｂｕｓ)中发现了ＩＳ1 1 2 [2 ] ,在带棒链霉菌 (Ｓ .ｃｌａｖｕｌｉｇｅｒｕｓ)中发现了ＩＳ1 1 6[3] ,…     

转座元件mariner

自mariner转座元件在Drosophila mauritiana中首次发现至今已经在包括人类在内的多种生物体中证实了mariner及类mariner元件（MLEs）的存在。MLEs属于mariner/Tc1超家族-II型转座元件中分布最广、种类最多的超家族之一。MLEs的转座酶都具有“D,D(34)D”的结构,并能催化MLEs通过“剪切和粘贴”机制进行转座。它们的宿主广泛和多样,能够进行种系传递,这都表明MLEs的转座不需要宿主特异元件的参与。 MLEs对多种生物尤其对脊椎动物的成功转化更支持了它们的不依赖宿主的转座机制,而且让人们看到了它们作为转基因载体的巨大潜能。 Abstract: Mariner and mariner-like elements (MLEs) have been found in a wide range of organisms including human since its discovery in Drosophila mauritiana. MLEs belong to the mariner/Tc1 superfamily, one of the most diverse and widespread Class II transposable elements. MLEs have a conserved “D,D(34)D” motif in their transposases and they transpose by cut-and-paste mechanisms. Their extraordinarily wide host range and horizontal transmission in distantly related species indicate that they do not need additional host-specific factors for transposition. The evidence that MLEs could transform a wide variety of organisms especially the vertebrates supported the host-independent mechanism and suggested the availability as a kind of potential transforming vector.     

Inference of Transposable Element Ancestry

Most common methods for inferring transposable element (TE) evolutionary relationships are based on dividing TEs into subfamilies using shared diagnostic nucleotides. Although originally justified based on the “master gene” model of TE evolution, computational and experimental work indicates that many of the subfamilies generated by these methods contain multiple source elements. This implies that subfamily-based methods give an incomplete picture of TE relationships. Studies on selection, functional exaptation, and predictions of horizontal transfer may all be affected. Here, we develop a Bayesian method for inferring TE ancestry that gives the probability that each sequence was replicative, its frequency of replication, and the probability that each extant TE sequence came from each possible ancestral sequence. Applying our method to 986 members of the newly-discovered LAVA family of TEs, we show that there were far more source elements in the history of LAVA expansion than subfamilies identified using the CoSeg subfamily-classification program. We also identify multiple replicative elements in the AluSc subfamily in humans. Our results strongly indicate that a reassessment of subfamily structures is necessary to obtain accurate estimates of mutation processes, phylogenetic relationships and historical times of activity.     

The Kinetics of Transposable Element Autoregulation

Kinetic modeling of the self-regulatory mechanisms of transposable elements (TEs) involving interactions of one or a few gene products makes predictions that are often at odds with observed results. In particular, explanations of TE autorepression at high copy number that invoke a decrease in number of active monomers through dimerization, amyloidization, and protein-mRNA binding to create an inactive state are not supported by analysis of the corresponding kinetic models. This is also true for similar mRNA–mRNA binding models. Self-repression in marineras well as other TEs can, however, be explained by a host-independent model in which inactive dimers compete with monomers for TE binding sites at the ends of the element. This model would also allow heterodimer poisoning to down-regulate transposition in the presence of divergent nonautonomous elements, since nondivergent monomers would be required at both TE ends for transposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tol1转座子研究进展

Tol1和Tol2是在青鳉基因组中发现的具有自主活性的DNA转座子,而Tol1转座子的自主活性是新近才发现的,因此对它的报道较少。较之Tol2,Tol1可以携带更大片段的DNA进行转座,且Tol1的转座不受转座酶"过量表达抑制"的影响。研究已证实,Tol1转座子在秀丽线虫、斑马鱼、爪蟾和人等多种生物中具有转座活性。因此,在动物转基因和基因功能研究等方面有重要的应用前景。从Tol1转座子的结构特征、转座机制和作为基因转移载体的优点,以及应用研究等方面进行了简要的综述。     

PASTEC: An Automatic Transposable Element Classification Tool

Summary

The classification of transposable elements (TEs) is key step towards deciphering their potential impact on the genome. However, this process is often based on manual sequence inspection by TE experts. With the wealth of genomic sequences now available, this task requires automation, making it accessible to most scientists. We propose a new tool, PASTEC, which classifies TEs by searching for structural features and similarities. This tool outperforms currently available software for TE classification. The main innovation of PASTEC is the search for HMM profiles, which is useful for inferring the classification of unknown TE on the basis of conserved functional domains of the proteins. In addition, PASTEC is the only tool providing an exhaustive spectrum of possible classifications to the order level of the Wicker hierarchical TE classification system. It can also automatically classify other repeated elements, such as SSR (Simple Sequence Repeats), rDNA or potential repeated host genes. Finally, the output of this new tool is designed to facilitate manual curation by providing to biologists with all the evidence accumulated for each TE consensus.

Availability

PASTEC is available as a REPET module or standalone software (http://urgi.versailles.inra.fr/download/repet/REPET_linux-x64-2.2.tar.gz). It requires a Unix-like system. There are two standalone versions: one of which is parallelized (requiring Sun grid Engine or Torque), and the other of which is not.     

Albinism Due to Transposable Element Insertion in Fish

The i locus of the medaka fish, Oryzias latipes, is responsible for tyrosinase expression, and several mutant alleles have been identified. The genotype i¹/i¹ exhibits a complete albino phenotype, having pale orange-red skin and red eyes. This mutant lacks in vivo tyrosinase activity. The genotype i⁴/i⁴, on the other hand, shows a quasi-albino phenotype with skin as bright as that of i¹/i¹ but with red-wine-colored eyes. At the light microscope level, reduced pigmentation is observed both in the skin and eyes of this mutant. The tyrosinase genes for the i¹ and the i⁴ alleles were cloned and sequenced, and compared with that of the wild-type tyrosinase gene. The i¹ allele was found to contain a 1.9-kb transposable element in the 1st exon, and the i⁴ allele was found to contain a 4.7-kb transposable element in the 5th exon. Both i¹ and i⁴ are alleles that were found in a commercial breeding population. The insertion of a transposable element thus appears to constitute a natural cause of mutations that cause albinism in this organism.