Homologous recombination and the repair of dna doublestrand. Homologous recombination and nonhomologous endjoining pathways of dna doublestrand break. The full text of this article is available as a pdf 764k. Nonhomologous end joining and homologous recombination dna. In the 15 years since gene targeting was demonstrated in vertebrate cells 14, it has been used extensively to investigate gene function and to create mouse models of human diseases. Nonhomologous dna end joining and alternative pathways to. It is most widely used by cells to accurately repair harmful breaks that occur on both strands of dna, known as double strand. Nonhomologous end joining and homologous recombination dna repair pathways in integration mutagenesis in the xylosefermenting yeast pichia stipitis. Homologous recombination and non homologous endjoining pathways of dna doublestrand break repair have overlapping roles in the maintenance of chromosomal integrity in vertebrate cells. Phagemediated homologous recombination systems, such as the bacteriophage. Homologous chromosomes refer to the chromosomes in the same pair while non.
Homologous recombination hr contributes to the repair of such dsbs in s and g2 phases, although it primarily functions following replication fork stalling or collapse 1,2. To understand human somatic mutation it is essential to know the relationship between these pathways in human cells. For homologous or general recombination, each homologous chromosome is shown as a different shade of blue and. Drosophila offers many advantages as an experimental organism. At least two distinct but overlapping pathways of dna repair are relevant to the execution of nonhomologous recombination. Molecular biology course, delivered by johannes walter on october 6, 2014. Consequently, multiple strategies have evolved to ensure that heteromorphic sex chromosomes are segregated. Dependence frequency homologous recombination on the. Immunoglobulin class switch recombination csr is initiated by a bcellspecific factor, activationinduced deaminase, probably through deamination of deoxycytidine residues within the switch s regions. Two major pathways operate in eukaryotic cells in the repair of endogenously or exogenously induced dsbs. Types of recombination recombination can occur between similar molecules of dna, as in homologous recombination, or dissimilar molecules, as in nonhomologous end joining nhej or ir.
However, in comparison with yeast and mouse, two other widely used eukaryotic model systems, drosophila suffers from an inability to perform homologous recombination between introduced dna and the corresponding chromosomal loci. Nonallelic homologous recombination nahr is a form of homologous recombination that occurs between two lengths of dna that have high sequence similarity, but are not alleles it usually occurs between sequences of dna that have been previously duplicated through evolution, and therefore have low copy repeats lcrs. Homologous recombination occurs naturally in eukaryotic organisms, bacteria, and certain viruses and is a powerful tool in genetic engineering. Homologous and nonhomologous chromosomes are the two types chromosomes identified based on the pairing pattern of chromosomes during the metaphase 1 of meiosis. Pdf nonhomologous dna end joining and alternative pathways. Nonhomologous recombination nhr is a major pathway for the repair of chromosomal doublestrand breaks in the dna of somatic cells. Homologous recombination 2014 weber state university.
Regulation of homologous recombination in eukaryotes. Pdf common fragile sites are specific loci that form gaps and constrictions on metaphase chromosomes exposed to replication stress, which. Deficiency in either of the breast cancer susceptibility proteins brca1 or brca2 induces profound cellular sensitivity to the inhibition of polyadpribose polymerase parp activity. Main difference homologous vs non homologous chromosomes. Removal of nonhomologous dna ends in doublestrand break. These repeat elements typically range from 10300 kb in length and share. Homologous chromosomes refer to the chromosomes in the same. Mechanism of homologous recombination springerlink. The ability to specifically modify the genomes of yeast and mouse provides a quick. Gene targeting by homologous recombination in drosophila. On the other hand, genetic recombination is the outcome of homologous recombination hr process, a housekeeping mechanism involved in the maintenance of genome integrity and generation of genetic.
Homologous recombination an overview sciencedirect topics. In meiosis, hr mediates the exchange of information between the maternal and paternal alleles within the gamete 230 san filippo sung klein annu. Homologous recombination is a ubiquitous process that plays a key role in the repair of dna damage and in restarting replication forks that have stalled or aborted as a consequence of the fork encountering dna lesions see cox 1998. Gene targeting in aspergillus fumigatus by homologous. Homologous recombination and nonhomologous endjoining repair. Effects of p53 status, microhomology, and repetitive dna length and orientation.
Surprisingly, the number of nonhomologous recombination events can be reduced if the polynucleotide is applied as a purified singlestranded dna. Ehmsen,1 and jie liu1 1department of microbiology, university of california, davis, davis, california 956168665. Thus, gene targeting is now a standard tool of somatic cell genetics, as it. Nonhomologous recombination in human cells molecular and. This method is based on the redet homologous recombination system, involving a. Homologous and nonhomologous recombination resulting in deletion. Each line represents a chromosome or segment of a chromosome. Nonhomologous end joining an overview sciencedirect. Homologous recombination in vivo is a more versatile and precise way to engineer large dna molecules 6, 98, 155. Nonhomologous recombination nhr, also called illegitimate recombination, was recognized initially and defined as genetic recombination that failed to show this canonical feature of hr, i. Doublestrand breaks dsbs in saccharomyces cerevisiae can be repaired by gene conversions or by deletions resulting from singlestrand annealing between direct repeats of homologous sequences. Homologous recombination and nonhomologous endjoining. Homologous recombination and non homologous endjoining oct 6, 2014 ericminikel boston, ma bcmp200 these are my notes from lecture in harvards bcmp 200. Us20080194029a1 method for increasing the ratio of.
Reca attaches to the resulting overhang homologous recombination model. Walter md, phd, in hematology, immunology and genetics third edition, 2019. Probability that a branch point of an intermediate is formed per site at t 0. Chen z, yang h, pavletich np 2008 mechanism of homologous recombination from the recassdnadsdna structures. Nonhomologous endjoining nhej is a ubiquitous doublestranded dna repair pathway and an important component of the process that diversifies the t and bcell receptor. Dna repair by nonhomologous end joining and homologous. Both homologous recombination and nhr pro cesses have an important role in the repair of dsbs, which are potentially lethalif left unrepaired 17, 28, 49. Pdf homologous recombination and nonhomologous endjoining. Hr leads to accurate repair, while nhej is intrinsically mutagenic. Abstract homologous recombination hr is an important mechanism for the repair of damaged chromosomes, for preventing the demise of. The present invention provides a method for increasing the ratio of homologous to nonhomologous recombination of a polynucleotide into a host cells dna by suppressing nonhomologous recombination. They load as a complex with each other and recc at a break. Thus, the total proportion of subjects with at least one lossoffunction germline or somatic homologous recombination mutation was 31% 115 of 367.
The two major pathways for repair of dna doublestrand breaks dsbs are homologous recombination hr and nonhomologous end joining nhej. Types of recombination recombination can occur between similar molecules of dna, as in homologous recombination, or dissimilar molecules, as in non homologous end joining nhej or ir. Though recombinational events are important for the proper functioning of most cells, little is known about the frequency and mechanisms of recombination in mammalian cells. We find that neither dna replication of the recombination substrate nor sv40 large t antigen is essential for either homologous or nonhomologous recombination involving viral or pbr322 sequences. Recombination in mitochondrial dna mtdna was documented more than 4 decades ago, but the underlying molecular mechanism has remained elusive. M takata, m s sasaki, e sonoda, c morrison, m hashimoto, h utsumi, y yamaguchiiwai, a shinohara, and s takeda. Mechanism of homologous recombination nyu langone health. Several independent products of homologous and nonhomologous recombination have been isolated and characterized at the dna sequence level. Homologous recombination hr provides a precise mechanism for targeting defined modifications to genomes in living cells. Homologous recombination is a universal process, conserved from bacteriophage to human, which is important for the repair of doublestrand dna breaks. Of homologous recombination homologous recombination hr, the exchange of genetic information between allelic sequences, has essential roles in meiosis and mitosis.
Information and translations of homologous recombination in the most comprehensive dictionary definitions resource on the web. Productive homologous and nonhomologous recombination of. In this lecture well cover homologous recombination hr, which uses the sister chromosome as a source of information, and nonhomologous. If the sequence that is used to initiate the bir mechanism is part of a repeatedsequence family and is located on a non homologous chromosome, bir can result in a nonreciprocal trans location. Homologous and non homologous chromosomes are the two types chromosomes identified based on the pairing pattern of chromosomes during the metaphase 1 of meiosis. Deficiency of human brca2 leads to impaired homologous recombination but maintains normal nonhomologous end joining. Nonhomologous end joining drives polyadpribose polymerase parp inhibitor lethality in homologous recombinationdeficient cells. Homologous recombination, the exchange of genetic material between two strands of dna that contain long stretches of similar base sequences.
Genetic engineering using homologous recombination. Productive homologous and nonhomologous recombination of hepatitis c virus in cell culture plos pathogens, mar 20 troels k. We have used simian virus 40 sv40pbr322 hybrid plasmids constructed in vitro as substrates to detect and quantitate intramolecular homologous and nonhomologous. Homologous recombination 799 table 1 symbols used symbol definition n homology length, ie. Disruption of the psku80 gene increased the frequency of homologous integration considerably but resulted in a remarkable decrease of the transformation efficiency. The akua gene encoding the ku70 component of the nonhomologous endjoining machinery was deleted in the opportunistic pathogen aspergillus fumigatus. Homologous recombination refers to dna exchange between two dna partners that share extensive sequence homology, as in two homologous chromosomes, for example. Chromosomes in the nucleus are the arrangement of genetic material of a particular cell. Homologous and nonhomologous recombination in monkey cells. Main difference homologous vs nonhomologous chromosomes. Specialized recombination called sitespecific recombination, first characterized in prokaryotes ssr is responsible for integration of phage genomes into the. Homologous and nonhomologous recombination resulting in.
Introduction homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of dna. In this study, a comparison was made between the nonhomologous end joining of transfected adenovirus dna fragments in vivo and the ability of purified human proteins to catalyze nonhomologous end joining in vitro. Homologous recombination is also exploited by organisms to generate genetic diversity in different ways, which include meiosis, mating type switching, and. No obvious phenotype could be assessed for the corresponding mutant strain but relative frequencies of homologous recombination were increased as deduced from targeting the laccaseencoding abr2 gene. Mechanism of homologous recombination and implications for. Comparison of nonhomologous end joining and homologous. Recent studies have revealed the presence of a rad52type recombination system of. Abundance of key proteins involved in nonhomologous dna end joining nhej, alternative end joining aej, singlestrand annealing ssa and homologous recombination hr. Homologous recombination starts with resection of the double strand breakage in the 5. Dna break repair by homologous recombination homologous. Deficiency in the repair of dna damage by homologous.
Nonhomologous end joining in class switch recombination. We hypothesized that the critical role of brca1 and brca2 in the repair of doublestrand breaks by homologous recombination hr was the underlying reason for this sensitivity. Definition of homologous recombination in the dictionary. The role of nonhomologous dna end joining, conservative. Here we show that replication stress leads to focus formation of rad51 and phosphorylated dnapkcs, key components of the homologous recombination hr. Recbcd role prepare the ds break end for hr homologous recombination function. Pdf dna doublestrand breaks dsbs are the most dangerous type of dna damage because they can result in the loss of large. Nhej modifies the broken dna ends, and ligates them together with little or no homology, generating deletions or insertions. Although rad1 mutants are resistant to xrays and can complete dsbmediated matingtype switching, they could not complete recombination when the ends of the break contained. Red system, have recently been exploited for these purposes 78, 94, 99, 156, 159. Meiotic recombination is 1001,000fold more frequent than mitotic recombination, and it usually involves homologous chromosomes and generates chromosomearm crossovers.