It is subject to mechanical stress and to many types of chemical modification that may lead to breaks in one or both strands of the double helix. This recombination usually occurs at a low frequency, but it is greatly enhanced by uv irradiation or other environmental stresses. Here, i concentrate on the analysis of the potential for illegitimate recombination in bacterial genomes. The integrity of genomic dna is crucial for its function. We previously demonstrated that a reverse transcript of a cellular reporter gene his3ai can serve as the donor for gene conversion of a chromosomal his3. Illegitimate recombination events produced either functional or non. A temperaturesensitive mutation in the lig gene reduced the frequency with which. Nonhomologous dna end joining, an event of illegitimate recombination, has been shown to occur more efficiently in s. Pdf illegitimate recombination, which is one of the major causes of genome rearrangements, can occur in a number. Illegitimate recombination occurs between dna sequences that are nonhomologous or have very short regions of homology, and is the result of.
Effect of the dna topoisomerase ii inhibitor vp16 on. Like mutation, genetic recombination contributes to a populationsgenetic diversity, which is. Integration of foreign dna during natural transformation of. Evolutionary dynamics and sites of illegitimate recombination.
A new type of illegitimate recombination is dependent on restriction and homologous interaction article pdf available in journal of bacteriology 17917. This insertion of genetic material which is not meant to be adjacent tends to lead to genes being broken causing the protein which they encode to not be properly expressed. However, targeting of nuclear genes has been an inefficient process in most eukaryotes, including algae, plants, and animals, due to the dominance of integration of the applied dna into nonhomologous. Sitespecific recombination occurs between a pair of strictly specified dna sequences, while transposition occurs between a specified sequence and a less specified sequence. Genetic recombination is a programmed feature of meiosis in most sexual organisms, where it ensures the proper segregation of chromosomes. Genetic recombination an overview sciencedirect topics. The first example of this specialized use of homologous recombination was. Photooxidative stress stimulates illegitimate recombination and mutability in carotenoid.
A characteristic feature of bacteriophage genomes is that they are architecturally mosaic, with each individual genome representing a unique assemblage of individual exchangeable modules. May 23, 2000 illegitimate recombination is a major cause of genetic instability in prokaryotes as well as in eukaryotes. The virion is nonenveloped, icosahedral, 1621nm in diameter and contains a closedcircular, ssdna genome of 1759 nucleotides nt, which makes it one of the smallest known animal viruses. Chromosomal dna transferred within a species can be integrated effectively by homologous recombination, whereas foreign dna with low or no sequence homology would rely on illegitimate recombination events, which are rare. Gene replacement by homologous recombination in plants holger puchta institut fur p. Illegitimate recombination is a natural process which was first found to be present within e. The frequency of illegitimate recombination has been measured by a. Pdf chromatin loops, illegitimate recombination, and. General or homologous recombination occurs between dna molecules.
These results suggest that vp16induced illegitimate recombination is of the same type as that occurring in the absence of drug. Low efficiency of homologyfacilitated illegitimate recombination. Paterson1,3,4 1plant genome mapping laboratory, university of georgia, athens, georgia 30602, usa. The active uptake of extracellular dna and its genomic integration is termed natural transformation and constitutes a major horizontal genetransfer mechanism in prokaryotes. Sitespecific recombinases ssrs perform rearrangements of dna segments by recognizing and binding to short dna sequences sites. Illegitimate recombination of dna is defined as recombi nation between sequences. Adenovirus serotype evolution is driven by illegitimate. In this paper, it is shown that recombination between phage. Under special conditions in escherichia coli, we have found a new type of illegitimate recombination that requires an interaction between.
Chromosomal breakpoint positions suggest a direct role for. Human lymphoid ccrfcem cells were treated with etoposide. Pdf chromatin loops, illegitimate recombination, and genome. In one embodiment of the invention, expression of an endogenous gene is activated or increased following integration into the cell, by nonhomologous or illegitimate recombination, of a regulatory sequence that activates expression of the gene. Nucleargene targeting by using singlestranded dna avoids. The linkage is not always complete, meaning that nonparental genotypes are seen in a proportion of the progeny. These might involve enzymes which cut and join dna or enzymes which replicate dna, as illustrated by two examples. It is thought that dna doublestrand breaks induced by this dna damage are important for initiation of illegitimate recombination. Six tdna inserts and their corresponding preinsertion sites were cloned from arabidopsis thaliana and analyzed. These rearrangements, which include deletion, duplication, and specialized transducing phage formation, fuse dna segments that were not. Pdf mitotic illegitimate recombination is a mechanism. Evolutionary dynamics and sites of illegitimate recombination revealed in the interspersion and sequence junctions of two nonhomologous satellite dnas in cactophilic drosophila species. Jan 18, 2016 sitespecific recombination sitespecific recombination, is a type of genetic recombination in which dna strand exchange takes place between segments possessing only a limited degree of sequence homology.
Ir was completely dependent on the nonhomologous endjoining nhej pathway for. Agrobacterium tumefaciens is a soil bacterium capable of transferring dna the tdna to the genome of higher plants, where it is then stably integrated. Msci target sequence, and that this process requires the yeast recombination gene rad52. The full text of this article is available as a pdf 1. Integration of foreign dna during natural transformation. In order to elucidate the mechanisms of illegitimate recombination in eukaryotes, we have studied the structure of dna fragments integrated by illegitimate recombination into the. Dna recombination is classified into four groups, depending on how sites of recombination are selected. Retroviruses have the potential to acquire host cellderived genetic material during reverse transcription and can integrate into the genomes of larger, more complex dna viruses. Dna, as well as conversion and duplication of dna sequences at junctions, suggests that t. Homologous dna recombination hr allows the deletion knockout, repair rescuing, and modification of a selected gene, thereby rendering a functional analysis of the gene product possible. In this way, some cells use legitimate recombination in the way other cells use illegitimate recombination. A 7001400 base pair segment of dna was found to have inserted itself into the gal and lac operons resulting in a strong polar mutation. At least four types of naturally occurring recombination have been identified in living organisms. Inhibition of dna topoisomerase ii may trigger illegitimate recombination in living cells.
In kluyveromyces lactis, integration of heterologous dna occurred very frequently therefore constituting an excellent model organism to study ir. Ir was completely dependent on the nonhomologous endjoining nhej pathway for dna double strand break dsb repair and we. In contrast, a simple model of illegitimate recombination may account for all of the junctions observed fig. Comparative inference of illegitimate recombination.
Reintroduction of the lig gene into this mutant restored the frequency of recombinant phage generation to that of wild type. Here we show that illegitimate recombination is enhanced by overexpression of the dnab protein in escherichia coli. We therefore conclude that illegitimate recombination induced by vp16 occurs between sequences of dna with short regions of homology. Dna damage by oxidative stress is one of the causes of mutagenesis. Streptococcus pneumoniae is a pathogen of global importance that frequently transfers genetic material between strains and on occasion across species boundaries.
An efficient method for random mutagenesis in mycobacterium avium subsp. In a second example, a dna segment has been recently acquired from the host bacterial chromosome by illegitimate recombination, providing further evidence that phage genomic mosaicism is generated by nontargeted recombination processes. Pdf a new type of illegitimate recombination is dependent. Recombination between similar but not identical dna. Illegitimate recombination falls into two classes, short homologyindependent and short homologydependent illegitimate recombination.
Illegitimate nonhomologous recombination requires little or no sequence homology between recombining dnas and has been regarded as being a process distinct from homologous recombination, which requires a long stretch of homology between recombining dnas. Nucleotide sequence comparison of wild type and tdnatagged genomic loci showed that tdna integration resulted in target site deletions of 2973 bp. Sometimes, 2 insertion sequences on different dna molecules will provide the homologous sequence needed to recombine the two example. Some viruses designated retroviruses integrate a dna version of their genome into chromosomes hiv and retroviruses.
Chromosomal breakpoint positions suggest a direct role for radiation in inducing illegitimate recombination between the ele1 and ret genes in. Illegitimate recombination definition of illegitimate. Hyperrecombination, diversity, and antibiotic resistance. Illegitimate dna integration in mammalian cells gene therapy. Genome organization porcine circovirus type 1 pcv1 is the type speci.
Dna recombination an overview sciencedirect topics. Pdf mechanisms of illegitimate recombination researchgate. This result suggests that the cleavage of dna by dna gyrase has a central role in the recombination process. In the absence of homologous regions, illegitimate recombination is thought to occur at a much higher rate in s. Illegitimate recombination dependent on t4 dna topoisomerase in a cellfree system has recently been described. Illegitimate recombination, by taking place between small repeats at short distances changes the chromosomal structure at a more local level although this can have global consequences. An appraisal of the potential for illegitimate recombination. To study the effect of oxidative stress on illegitimate recombination, we examined the frequency of. Two tdna integration events from nicotiana tabacum were included in the analysis. Homology between short segments within target sites and t. A laboratory manual, second edition cold spring harbor, new. The ability to target homologous recombination by ds breaks has also been utilized by different kinds of cells as a means of altering the proteins they express.
In contrast, rna viruses were believed not to integrate into the hosts genome under any circumstances. The homologous and illegitimate products are also generated in nuclear extracts from stage vi xenopus oocytes. These results indicate that hdf1 is involved in illegitimate recombination, but not in homologous recombination. Comparative inference of illegitimate recombination between. Structural analyses of dna fragments integrated by. This mechanism was then found to have the ability to insert other short genetic sequences into other locations within the bacterial genome often.
Common sites for recombination and cleavage mediated by e. We studied the role of dna ligase in illegitimate recombination in escherichia coli. Plausible mechanisms for generating mosaicism include homologous recombination at shared boundary sequences of module junctions, illegitimate recombination in a nonsequencedirected process, and. Genome wide distribution of illegitimate recombination events. Topoisomerase i has been suspected of causing chromosome aberrations by mediating illegitimate recombination. Because etoposideassociated aml is characterized by sitespecific illegitimate dna recombination, we studied whether etoposide could directly cause sitespecific deletions of exons 2 and 3 in the hprt gene. The rate of illegitimate recombination is shown to be reduced in the hdf1 disruptant. Volume 5, issues 12, 15 december 1993, pages 161166.
Chromosomal dna transferred within a species can be integrated effectively by homologous recombination, whereas foreign dna with low or no sequence homology would rely on illegitimate. Mechanisms of illegitimate recombination sciencedirect. Here, we report our findings about the pattern and frequency of illegitimate recombination by answering the following questions. Letter comparative inference of illegitimate recombination between rice and sorghum duplicated genes produced by polyploidization xiyin wang,1,2 haibao tang,1,3 john e. This is explained by crossing over between the gene pairs during meiosis in the parents. Illegitimate recombination, or nonhomologous recombination, is the process by which two unrelated double stranded segments of dna are joined. Enzymes known as sitespecific recombinases ssrs perform rearrangements of dna segments by recognizing and binding to short, specific dna sequences sites. Gene replacement by homologous recombination in plants. Illegitimate recombination that usually takes place at a low frequency is greatly enhanced by treatment with dnadamaging agents. Bacterial recombination genetic recombination refers to the exchange of genes between twodna molecules to form new combinations of genes on achromosome. Sitespecific recombination, also known as conservative sitespecific recombination, is a type of genetic recombination in which dna strand exchange takes place between segments possessing at least a certain degree of sequence homology. Genomic characterization of mycobacteriophage giles. Precise excision of tn10 and related transposons occurs by recombination between directly repeated 9 bp sequences that flank the transposon.
Schnurr viral and rickettsial disease laboratory, division of communicable disease control, california department of health services, berkeley. In an analysis of 1930 pneumococcal genotypes from six housekeeping genes and 94 genotypes from related species, we identified mosaic genotypes representing admixture between populations and found that these were. Genome wide distribution of illegitimate recombination. Role of dna ligase in the illegitimate recombination that. Recombination of retrotransposon and exogenous rna virus. Some molecules undergo homologous recombination by a resectionannealing mechanism. However, whether or not dna damage induces illegitimate recombination has not been determined. Sitespecific recombination sitespecific recombination, is a type of genetic recombination in which dna strand exchange takes place between segments possessing only a limited degree of sequence homology. The involvement of cellular recombination and repair genes. Illegitimate recombination ir is the process by which two dna molecules not sharing homology to each other are joined. Illegitimate recombination induced by overproduction of. Illegitimate recombination induced by overproduction of dnab.
Chromatin loops, illegitimate recombination, and genome evolution. A new type of illegitimate recombination is dependent on. Genetic recombination refers to the rearrangement of dna sequences by some combination of the breakage, rejoining, and copying of chromosomes or chromosome segments. We also show that the hdf1 mutation does not affect mitotic and meiotic homologous recombination. Dna integration results from illegitimate recombination. Transferred dna tdna insertions of agrobacterium gene fusion vectors and corresponding insertional target sites were isolated from transgenic and wild type arabidopsis thaliana plants. Illegitimate recombination, or nonhomologous recombination, is the process by which two.
Illegitimate recombination can repair dna doublestrand breaks in one of two ways, either without sequence homology or by using a few base pairs of homology at the junctions. We found that illegitimate recombination between an exogenous nonretroviral rna virus, lymphocytic. Illegitimate recombination mediated by doublestrand break. Rad1, rad10 and rad52 mutations reduce the increase of. Illegitimate recombination, which is one of the major causes of genome rearrangements, can occur in a number of ways. Dna damages produced by these environmental stresses are thought to induce dna doublestrand breaks, leading to illegitimate recombination.
Illegitimate recombination in bacteria and bacteriophage illegitimate recombination in bacteria and bacteriophage weisberg, r a. Insertion of a mobile genetic element into a target chromosome. Illegitimate recombination has been regarded as a process distinct from. Illegitimate recombination involves no homology between the participating dna molecules.
The second process is known as microhomologymediated recombination. In this study, we examine the involvement of other recombination and repair genes in rnamediated recombination, and gain insight into the. Dna molecules were produced by the topoisomerase alone, without an escherichia coli extract. Lecturer in the school of biological sciences, university of sussex. In order to elucidate the mechanisms of illegitimate recombination in eukaryotes, we have studied the structure of dna fragments integrated by illegitimate recombination into the genome of fission yeast. Recombination of dna assortment, leading to the conclusion that those genes are linked on a chromosome. The excision, which is a model for a class of illegitimate dna recombination events, was stimulated 106 times by induction of singlestranded dna synthesis, occurred during conversion of singlestranded dna to doublestranded form, and entailed no. Short homologies between the tdna ends and the target sites, as well as the presence of filler sequences at the junctions, indicate that tdna integration is mediated by illegitimate recombination and that these processes in plants are very analogous to events in mammalian cells. Silencing factors participate in dna repair and recombination. Chromosomal illegitimate recombination in mammalian cells is associated with intrinsically bent dna elements. And yet, dna in living cells is inherently unstable. Previous studies showed that ionizing radiation and restriction enzymes increase the frequency of microhomologymediated recombination in trans during. Escherichia coli mutm suppresses illegitimate recombination.
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