GO:0000727 double-strand break repair via break-induced replication: Mechanism, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000727 describes an error-free homologous recombination pathway that repairs a one-ended DNA double-strand break by copying an intact homologous chromosome to the end of the chromosome.
• Break-induced replication (BIR) is initiated by resection of the broken end, invasion of the 3' single-stranded DNA into a homologous template, and assembly of a migrating D-loop that drives conservative DNA synthesis.
• BIR is distinct from gene conversion because it can copy hundreds of kilobases and frequently leads to loss of heterozygosity, non-reciprocal translocations, and complex genomic rearrangements.
• Key proteins include RAD51, RAD52, RAD54, the Pol32 subunit of DNA polymerase delta, PIF1 helicase, and the MCM helicase complex, which together coordinate strand invasion, bubble migration, and processive synthesis.
• Deregulated BIR contributes to cancer genome instability, telomere maintenance in alternative lengthening of telomeres (ALT) cancers, and structural variation in somatic cells.
• CRISPR-based knockout, point-mutation, knock-in, and overexpression models enable causal dissection of BIR genes in human cells and are supported by EDITGENE services.
Description
Double-strand breaks (DSBs) are among the most cytotoxic DNA lesions, and cells repair them through multiple pathways including non-homologous end joining, homologous recombination, and break-induced replication (BIR). GO:0000727, double-strand break repair via break-induced replication, defines a specific homologous recombination subpathway that repairs a one-ended DSB when only one side of the break has a homologous template, such as at a collapsed replication fork, an eroded telomere, or a chromosome fragment lacking a centromere. Unlike classical gene conversion, BIR uses the intact chromosome as a template and synthesizes DNA processively to the end of the chromosome, often copying hundreds of kilobases. This process is error-free in its template-dependent synthesis but is inherently mutagenic because the migrating D-loop can dissociate, template-switch, or generate complex rearrangements. BIR was first characterized in yeast and has since been recognized as a conserved mechanism in eukaryotes, including human cells, where it contributes to alternative lengthening of telomeres (ALT) and to genomic instability in cancer. The pathway is initiated by 5' to 3' resection of the broken end, yielding a 3' single-stranded DNA tail that is bound by RAD51 and other recombination factors. Strand invasion creates a D-loop that is converted into a migrating bubble, within which DNA synthesis by polymerase delta proceeds conservatively, meaning the newly synthesized strand is displaced from the template as a single-stranded flap. This conservative mode of synthesis distinguishes BIR from semi-conservative replication and has important implications for how mutations and rearrangements arise. For researchers, GO:0000727 provides a precise ontological handle for annotating genes, designing functional assays, and interpreting genome-wide screens that interrogate DSB repair. Because BIR is implicated in cancer, aging, and genome evolution, tools to manipulate BIR genes in human cell models are essential for mechanistic and translational studies. This article summarizes the definition, mechanism, key genes, disease links, and research methods for GO:0000727, with a focus on how CRISPR-based cell models can accelerate discovery.
double-strand break repair via break-induced replication At A Glance
| GO ID | GO:0000727 |
|---|---|
| GO term | double-strand break repair via break-induced replication |
| Ontology | biological_process |
| Synonym | none |
| Major function | Error-free repair of a one-ended double-strand break by homologous recombination using an intact chromosome as a template, with DNA synthesis from the 3' invading strand to the chromosome end |
| Alternative names | BIR; break-induced replication |
| Key initiating event | 5' to 3' end resection generating a 3' single-stranded DNA tail |
| Key synthesis mode | Conservative DNA synthesis within a migrating D-loop bubble |
| Cellular contexts | Collapsed replication forks, eroded telomeres, one-ended DSBs, and chromosome fragments |
What Is GO:0000727?
GO:0000727, double-strand break repair via break-induced replication, is a biological process in which a double-strand break is repaired by homologous recombination using an intact homologous chromosome as a template. The centromere-proximal end of the broken chromosome invades the intact homolog, and DNA synthesis initiates from the 3' end of the invading strand and continues to the end of the chromosome. This mechanism is error-free with respect to the template but can produce loss of heterozygosity and rearrangements because it copies long stretches of DNA non-reciprocally.
Why Is double-strand break repair via break-induced replication Important in Cell Biology?
GO:0000727 is important because BIR is a major homology-directed repair pathway for one-ended DSBs that cannot be repaired by canonical homologous recombination, and its deregulation is a source of genomic instability in cancer and aging. Understanding BIR is essential for interpreting mutational signatures, structural variants, and telomere maintenance mechanisms, and for developing therapies that exploit BIR dependencies in tumors.
• BIR repairs one-ended DSBs that arise at collapsed replication forks, which are common in cancer cells with replication stress.
• BIR drives alternative lengthening of telomeres (ALT), a telomerase-independent telomere maintenance mechanism in a subset of cancers.
• BIR can generate loss of heterozygosity, non-reciprocal translocations, and complex genomic rearrangements.
• BIR is a source of clustered mutations and template-switching events that contribute to kataegis and mutational signatures.
• BIR is conserved from yeast to humans, making model organisms valuable for mechanistic studies.
• BIR is implicated in genome evolution and in the formation of structural variants in somatic cells.
• BIR proteins such as RAD51, RAD52, and PIF1 are potential therapeutic targets in cancers with BIR dependencies.
• BIR is a key pathway for understanding how cells tolerate replication stress and DNA damage.
• BIR assays are used in genome-wide screens to identify novel DSB repair factors.
• BIR dysfunction may contribute to neurodegeneration through accumulation of DNA damage.
What Happens During double-strand break repair via break-induced replication?
Initiation by end resection
In simple terms: The broken DNA end is chewed back to expose a single-stranded tail that can search for a matching sequence.
BIR begins with 5' to 3' resection of the broken DNA end, generating a 3' single-stranded DNA (ssDNA) tail. This resection is mediated by the MRN complex and CtIP in human cells, and by the Exo1 and Dna2 nucleases, and is coupled to the action of the WRN helicase. The resulting ssDNA is coated by RPA and subsequently by RAD51 to form a nucleoprotein filament that can invade a homologous template. Resection is a regulated step and determines whether the break is channeled into BIR or other repair pathways.
Strand invasion and D-loop formation
In simple terms: The single-stranded tail inserts itself into the matching sequence on the intact chromosome, forming a loop.
The RAD51-ssDNA filament searches for homology and invades the intact homologous chromosome, forming a displacement loop (D-loop). RAD54 and other accessory factors stabilize the joint molecule and promote strand exchange. In BIR, the D-loop is unusual because it is a one-ended invasion that lacks a second end to capture, so it must be converted into a replication fork-like structure.
Migrating bubble and conservative DNA synthesis
In simple terms: The loop moves along the chromosome while new DNA is made, and the new strand is pushed out as a separate tail.
The D-loop is converted into a migrating bubble in which DNA synthesis by polymerase delta, with its Pol32 subunit, proceeds conservatively. The newly synthesized strand is displaced as a single-stranded flap, and the bubble migrates along the template. This conservative mode of synthesis is a hallmark of BIR and distinguishes it from normal semi-conservative replication. The PIF1 helicase and the MCM complex are required for processive bubble migration.
Processive synthesis to the chromosome end
In simple terms: The copying continues all the way to the end of the chromosome, potentially copying hundreds of thousands of bases.
BIR synthesis can proceed for hundreds of kilobases to the end of the chromosome, making it highly processive. This long-range synthesis is facilitated by the MCM helicase and by recombination proteins that maintain the migrating bubble. The process is error-free with respect to the template but can be interrupted by template switching, leading to complex rearrangements.
Resolution and consequences
In simple terms: When copying finishes, the new DNA is joined to the broken chromosome, but the process can leave behind rearrangements.
Upon reaching the chromosome end, the newly synthesized strand is ligated to the broken chromosome, completing repair. However, BIR frequently generates non-reciprocal translocations, loss of heterozygosity, and complex structural variants because the copied region is not exchanged reciprocally. In human cells, unscheduled BIR can lead to genomic rearrangements and is associated with cancer.
Key Genes Involved in GO:0000727 double-strand break repair via break-induced replication
The following genes and proteins are core components or regulators of GO:0000727, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| RAD51 | Forms nucleoprotein filament on ssDNA and catalyzes strand invasion | Central to BIR initiation; knockout is lethal in vertebrates, so conditional models are used |
| RAD52 | Mediates strand annealing and D-loop formation; supports BIR | Potential target in cancers with BIR dependencies |
| RAD54 | Chromatin remodeler that stabilizes D-loop and promotes strand exchange | Used to study BIR efficiency and recombination intermediate stability |
| POL32 (POLD3 in humans) | Subunit of DNA polymerase delta required for BIR synthesis | Key marker of BIR activity; knockout reduces BIR and ALT |
| PIF1 | Helicase that promotes migrating bubble and processive synthesis | Regulates BIR processivity and telomere maintenance |
| MCM2-7 | Replicative helicase complex required for BIR bubble migration | Links BIR to replication machinery; target for inhibitor studies |
| RAD18 | E3 ubiquitin ligase that mediates DSB-induced ubiquitination | Regulates chromatin response to DSBs and BIR-associated repair |
| WRN | RecQ helicase that facilitates mitotic DNA synthesis and resection | Implicated in Werner syndrome and BIR-related repair |
| EXO1 | Nuclease that performs long-range resection | Determines extent of resection and BIR initiation |
| DNA2 | Nuclease/helicase involved in resection | Cooperates with EXO1 in end processing |
| BLM | RecQ helicase that regulates recombination and BIR | Mutations cause Bloom syndrome with genome instability |
| RPA | Binds ssDNA and protects it during resection | Essential for BIR initiation; used in biochemical assays |
| MRE11 | Part of MRN complex that initiates resection | Target for studying resection initiation |
| NBS1 | Part of MRN complex; recruits ATM and resection factors | Mutations cause Nijmegen breakage syndrome |
| ATM | Kinase that coordinates DSB response and resection | Regulates BIR choice and cell cycle checkpoints |
| ATR | Kinase that responds to ssDNA and replication stress | Modulates BIR under replication stress |
| PCNA | Sliding clamp that supports polymerase processivity | Required for BIR synthesis; used in replisome studies |
How Is double-strand break repair via break-induced replication Regulated?
BIR is regulated at multiple levels. Cell cycle stage controls resection and BIR, with BIR occurring primarily in S and G2 phases when a sister chromatid or homolog is available. The ATM and ATR kinases coordinate the DNA damage response and influence the choice between BIR and other repair pathways. Ubiquitination of chromatin proteins by RAD18 modulates the accessibility of the break to repair factors. The PIF1 helicase and MCM complex regulate the processivity of the migrating bubble, and their activity is coupled to replication fork proteins. In addition, telomere-binding proteins regulate BIR at telomeres, which is relevant to ALT cancers.
double-strand break repair via break-induced replication and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| RAD51 | Cancer predisposition, genome instability | Knockout or point-mutation in human cell lines; conditional KO in mice |
| RAD52 | Cancer, ALT dependency | Knockout and overexpression in ALT cancer cell lines |
| WRN | Werner syndrome, premature aging | Patient-derived fibroblasts; CRISPR knock-in of patient mutations |
| BLM | Bloom syndrome, cancer predisposition | Knockout in human cells; knock-in of BLM mutations |
| POLD3 | Cancer, BIR deficiency | Knockout in cancer cell lines; overexpression for BIR assays |
Cancer and genome instability
Deregulated BIR is a major source of genomic rearrangements in cancer, including non-reciprocal translocations, loss of heterozygosity, and complex structural variants. BIR is also the mechanism underlying alternative lengthening of telomeres (ALT) in a subset of tumors, making BIR proteins potential therapeutic targets. Mutations in BIR genes such as RAD51, RAD52, and BLM are associated with cancer predisposition and genome instability syndromes.
Neurodegeneration
Defects in DSB repair, including BIR, can lead to accumulation of DNA damage in post-mitotic neurons, contributing to neurodegeneration. Although direct evidence for BIR in neurons is limited, the broader homologous recombination machinery is implicated in neuronal survival.
Premature aging and telomere disorders
WRN helicase, which facilitates resection and mitotic DNA synthesis, is mutated in Werner syndrome, a premature aging disorder. BIR at telomeres is linked to telomere maintenance and dysfunction, and dysregulated BIR can contribute to telomere-driven pathologies.
From double-strand break repair via break-induced replication-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is a candidate gene required for BIR? | CRISPR knockout in human cell lines followed by BIR reporter assay |
| Does a specific point mutation affect BIR efficiency? | CRISPR point-mutation knock-in of the variant |
| Does a gene fusion or tag affect BIR protein localization? | CRISPR knock-in of fluorescent or epitope tag |
| Does overexpression of a BIR gene increase BIR? | CRISPR overexpression or lentiviral overexpression |
| Which genes are synthetic lethal with BIR deficiency? | CRISPR library screening in BIR-deficient background |
| What is the transcriptional response to BIR induction? | RNA-seq after site-specific DSB induction |
How to Study the double-strand break repair via break-induced replication Process
| Method | What It Measures | Typical Application |
|---|---|---|
| BIR reporter assay | Frequency of BIR-mediated repair | Testing gene requirements for BIR |
| Whole-genome sequencing | Structural variants and loss of heterozygosity | Detecting BIR-associated rearrangements |
| RNA-seq | Transcriptional changes after DSB induction | Identifying BIR-regulated genes |
| ChIP-seq | Binding of BIR proteins at damage sites | Mapping RAD51 and Pol32 recruitment |
| Mass spectrometry | Protein interactions and modifications | Identifying BIR complex components |
| Live-cell imaging | Dynamics of BIR foci and bubble migration | Real-time BIR monitoring |
| CRISPR library screening | Genes required for BIR or synthetic lethality | Genome-wide discovery of BIR factors |
BIR reporter assays
BIR is commonly measured using plasmid- or chromosome-based reporters that contain a single double-strand break with only one homologous arm, so repair must occur by BIR. These assays can be coupled to restriction enzyme-induced DSBs or CRISPR-Cas9 cleavage to quantify BIR frequency and product structure.
Genomic and sequencing approaches
Whole-genome sequencing, long-read sequencing, and optical mapping can detect BIR-associated structural variants such as non-reciprocal translocations and loss of heterozygosity. Break-seq and related methods map DSB sites and repair outcomes genome-wide.
Proteomics and interactomics
Affinity purification coupled to mass spectrometry can identify BIR protein complexes and post-translational modifications, such as RAD18-mediated ubiquitination. Proximity labeling can map the BIR interactome at sites of damage.
Imaging and single-molecule analysis
Live-cell imaging of fluorescently tagged BIR proteins and DNA repair foci allows real-time monitoring of strand invasion and bubble migration. Single-molecule assays can measure helicase and polymerase activities on model BIR substrates.
How CRISPR Can Be Used to Study GO:0000727 double-strand break repair via break-induced replication
Knockout
CRISPR knockout of BIR genes such as RAD52, POLD3, or PIF1 in human cell lines can reveal their requirement for BIR and ALT. Knockout models are also used to test synthetic lethality with other repair defects.
Point Mutation
CRISPR point-mutation knock-in can model disease-associated variants in BIR genes, such as RAD51 or BLM mutations, to assess their impact on BIR efficiency and genome stability.
Knock-in
Knock-in of fluorescent or epitope tags at endogenous loci enables visualization and biochemical isolation of BIR proteins without overexpression artifacts. Knock-in of inducible degrons allows rapid depletion of essential BIR factors.
Overexpression
CRISPR-mediated overexpression or lentiviral overexpression of BIR genes can test whether increased dosage promotes BIR, ALT, or genome instability. Overexpression models are useful for studying dominant-negative or gain-of-function variants.
How EDITGENE Supports double-strand break repair via break-induced replication Research
Researchers studying double-strand break repair via break-induced replication-related genes often need to determine whether a candidate gene is causally involved in BIR, how a specific variant affects repair, or whether overexpression alters genome stability. EDITGENE provides end-to-end CRISPR cell model services to answer these questions with publication-ready rigor.
Contact EDITGENE today to design your custom CRISPR model for double-strand break repair via break-induced replication research.
Frequently Asked Questions About double-strand break repair via break-induced replication
What is double-strand break repair via break-induced replication?
It is a homologous recombination pathway defined by GO:0000727 that repairs a one-ended double-strand break by invading an intact homologous chromosome and synthesizing DNA to the chromosome end.
What genes are involved in break-induced replication?
Key genes include RAD51, RAD52, RAD54, POLD3 (POL32), PIF1, MCM2-7, RAD18, WRN, EXO1, DNA2, BLM, RPA, MRE11, NBS1, ATM, ATR, and PCNA.
How is break-induced replication different from homologous recombination?
BIR repairs one-ended breaks and copies long stretches of DNA non-reciprocally, whereas canonical homologous recombination typically involves two-ended breaks and reciprocal exchange.
What is the role of RAD51 in break-induced replication?
RAD51 forms a nucleoprotein filament on single-stranded DNA and catalyzes invasion of the homologous template, a required step for BIR.
What is a migrating bubble in BIR?
A migrating bubble is the D-loop-derived structure in which DNA synthesis occurs conservatively, with the new strand displaced as a single-stranded flap.
Is break-induced replication error-free?
BIR synthesis is error-free with respect to the template, but the pathway can generate loss of heterozygosity and complex rearrangements.
How is break-induced replication measured in the lab?
Common assays include plasmid- or chromosome-based BIR reporters, whole-genome sequencing for structural variants, and imaging of repair foci.
What diseases are linked to break-induced replication?
BIR is linked to cancer genome instability, alternative lengthening of telomeres, and premature aging disorders such as Werner syndrome.
Can CRISPR be used to study break-induced replication?
Yes, CRISPR knockout, point-mutation knock-in, tagged knock-in, and overexpression models are widely used to dissect BIR gene function.
What is the GO ID for break-induced replication?
The Gene Ontology ID is GO:0000727, double-strand break repair via break-induced replication.
Conclusion
GO:0000727, double-strand break repair via break-induced replication, defines a conserved homologous recombination pathway that repairs one-ended DSBs by copying an intact chromosome. Its unique migrating-bubble mechanism and conservative synthesis make it a major source of genomic rearrangements and a key pathway in cancer and telomere maintenance. CRISPR-based cell models are powerful tools for dissecting BIR gene function and for translating these insights into therapeutic strategies.
References
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- 3. Barwacz SA et al.. 2025. DNA double-strand break end resection factors and WRN facilitate mitotic DNA synthesis in human cells.. Nat Commun 16(1):7901 PMID: 40854910
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