GO:0031391 Elg1 RFC-like complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031391 describes the Elg1 RFC-like complex, a pentameric clamp unloader that removes PCNA from chromatin [1, 4, 6].
• In Saccharomyces cerevisiae, the complex comprises Elg1p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p, sharing four subunits with the canonical RFC clamp loader [4, 6].
• Elg1-RFC is a guardian of genome stability, with roles in telomere length regulation, DNA damage checkpoint activation, and suppression of recombination [1, 2, 7].
• The human homolog of Elg1 is ATAD5, and the ATAD5 RFC-like complex is a major PCNA unloader in vertebrates [3, 8].
• Dysregulation of PCNA unloading is linked to cancer and genome instability disorders, making Elg1-RFC a potential therapeutic target.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models are essential to dissect Elg1-RFC function in health and disease [1, 2, 4].
Description
The Elg1 RFC-like complex (GO:0031391) is a conserved pentameric replication factor C (RFC)-like complex that functions as a PCNA unloader, removing the DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) from chromatin [1, 4, 6]. First identified in Saccharomyces cerevisiae through genetic screens for genome instability, Elg1 (enhanced level of genomic instability) forms an alternative RFC complex with the small RFC subunits Rfc2p, Rfc3p, Rfc4p, and Rfc5p [4, 6]. Unlike the canonical RFC clamp loader that loads PCNA onto DNA during replication, the Elg1 RFC-like complex unloads PCNA after replication completion or in response to DNA damage, thereby maintaining genome stability [1, 8]. This complex is critical for telomere length regulation, DNA damage checkpoint activation, and prevention of unscheduled recombination [1, 2, 7]. In higher eukaryotes, the Elg1 homolog ATAD5 (also known as ELG1) forms a similar RFC-like complex that is the major PCNA unloader in Xenopus egg extracts and human cells [3, 8]. Understanding the Elg1 RFC-like complex is therefore central to deciphering how cells preserve genomic integrity and how its dysfunction contributes to cancer and other genome instability syndromes.
Elg1 RFC-like complex At A Glance
| GO ID | GO:0031391 |
|---|---|
| GO term | Elg1 RFC-like complex |
| Ontology | cellular_component |
| Synonym | Elg1-RFC, Elg1-RLC, RFC (Elg1) |
| Major function | Unloads PCNA from chromatin; maintains genome stability; regulates telomere length |
| Subunits (S. cerevisiae) | Elg1p, Rfc2p, Rfc3p, Rfc4p, Rfc5p |
| Human homolog | ATAD5 (ELG1) forms an RFC-like complex with RFC2-5 |
| Related processes | DNA replication, DNA damage checkpoint, telomere maintenance, homologous recombination |
What Is GO:0031391?
The Elg1 RFC-like complex is a pentameric protein complex that belongs to the replication factor C (RFC) family of AAA+ ATPases. It is defined by its ability to unload PCNA from chromatin, a function opposite to that of the canonical RFC clamp loader. In Saccharomyces cerevisiae, the complex consists of the large subunit Elg1p and the four small subunits Rfc2p, Rfc3p, Rfc4p, and Rfc5p. This complex plays roles in telomere length regulation and other aspects of genome stability, including the DNA damage response and suppression of homologous recombination [1, 4, 6].
Why Is Elg1 RFC-like complex Important in Cell Biology?
The Elg1 RFC-like complex is a key regulator of genome stability, acting as the primary PCNA unloader to ensure proper termination of DNA replication and prevent aberrant recombination [1, 8]. Its importance is underscored by the observation that loss of Elg1 leads to increased genomic instability, sensitivity to DNA-damaging agents, and defects in telomere length regulation [1, 4]. In humans, the Elg1 homolog ATAD5 is frequently downregulated in cancers and is essential for maintaining genomic integrity. Moreover, the complex is required for eliciting the DNA damage checkpoint, linking PCNA unloading to cell cycle arrest and repair [2, 7]. Thus, studying Elg1-RFC provides insights into fundamental mechanisms of DNA replication and repair, with direct implications for cancer biology and potential therapeutic strategies.
• Maintains genome stability by unloading PCNA from chromatin after replication [1, 4].
• Regulates telomere length and prevents telomere dysfunction.
• Required for activation of the DNA damage checkpoint in response to replication stress [2, 7].
• Suppresses homologous recombination and prevents unscheduled recombination events.
• Its human homolog ATAD5 is frequently downregulated in cancers and is associated with genome instability.
• Plays a role in the response to DNA-damaging agents such as methyl methanesulfonate (MMS) and hydroxyurea [4, 5].
• Coordinates with other RFC-like complexes (Ctf18-RFC) to ensure proper replication fork progression.
• Serves as a model for understanding AAA+ ATPase function in clamp unloading.
• Potential target for cancer therapy due to its role in maintaining genomic integrity.
• Essential for understanding the interplay between PCNA unloading and cell cycle checkpoints [2, 7].
Elg1 RFC-like complex: Biological Process, Cellular Component, and Molecular Function
What Happens During Elg1 RFC-like complex?
In simple terms: The Elg1 RFC-like complex acts like a molecular wrench that removes PCNA, a sliding clamp that holds DNA polymerase onto DNA, after replication is finished or when DNA is damaged.
The primary biological process mediated by the Elg1 RFC-like complex is the unloading of PCNA from chromatin [1, 4]. During DNA replication, PCNA is loaded onto DNA by the canonical RFC clamp loader to enhance polymerase processivity. After replication termination or upon encountering DNA damage, Elg1-RFC recognizes PCNA on chromatin and catalyzes its removal in an ATP-dependent manner [1, 8]. This unloading is crucial for preventing PCNA from remaining on DNA, which could lead to inappropriate recruitment of DNA repair and recombination factors. Additionally, Elg1-RFC is involved in telomere length regulation, as its deletion leads to telomere elongation defects. The complex also plays a role in eliciting the DNA damage checkpoint, as cells lacking Elg1 fail to properly activate the checkpoint kinase Rad53 in response to replication stress [2, 7].
Structure and Composition of Elg1 RFC-like complex
In simple terms: The Elg1 RFC-like complex is made of five proteins: one large subunit called Elg1 and four small subunits that are shared with the canonical RFC clamp loader.
In Saccharomyces cerevisiae, the Elg1 RFC-like complex is a pentameric assembly composed of the large subunit Elg1p and the four small subunits Rfc2p, Rfc3p, Rfc4p, and Rfc5p [4, 6]. The small subunits are shared with the canonical RFC clamp loader, but the large subunit Elg1p replaces Rfc1p, the large subunit of the canonical RFC. This substitution confers the unique PCNA unloading activity to the complex. The complex is a member of the AAA+ ATPase family, and its ATPase activity is essential for PCNA unloading. In humans, the Elg1 homolog ATAD5 forms a similar complex with RFC2-5, and this complex is the major PCNA unloader in Xenopus egg extracts.
Molecular Mechanism of Elg1 RFC-like complex
In simple terms: The Elg1 RFC-like complex uses energy from ATP to grab PCNA and pull it off DNA, a process that requires specific interactions between the complex and PCNA.
The molecular mechanism of PCNA unloading by Elg1-RFC involves ATP binding and hydrolysis, which drive conformational changes in the complex that lead to PCNA release. Elg1p contains a PCNA-interacting peptide (PIP) motif that mediates direct binding to PCNA. The complex recognizes PCNA that is either free on DNA or in complex with DNA polymerase, and through a series of ATP-dependent steps, it opens the PCNA ring and removes it from DNA [1, 8]. This activity is regulated by the DNA damage checkpoint and is important for preventing replication fork stalling and collapse [2, 7]. The human ATAD5 complex similarly uses ATP to unload PCNA, and its activity is essential for maintaining genome stability.
Regulation of Elg1 RFC-like complex
In simple terms: The activity of the Elg1 RFC-like complex is controlled by cellular signals that respond to DNA damage and replication stress.
The Elg1 RFC-like complex is regulated at multiple levels. Its expression is induced by DNA-damaging agents and replication stress, partly through the DNA damage checkpoint pathway [2, 7]. In Saccharomyces cerevisiae, Elg1p levels increase upon treatment with methyl methanesulfonate (MMS) or hydroxyurea, and this induction is dependent on the checkpoint kinases Mec1 and Rad53. Additionally, the complex's activity may be modulated by post-translational modifications, although specific modifications remain to be fully characterized. The human ATAD5 protein is also regulated by ubiquitination and its stability is linked to the DNA damage response. Overall, the regulation ensures that PCNA unloading is tightly coupled to replication completion and DNA repair.
Key Genes Involved in GO:0031391 Elg1 RFC-like complex
The following genes and proteins are key components or regulators of the Elg1 RFC-like complex and its associated functions.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ELG1 (S. cerevisiae) | Large subunit of the Elg1 RFC-like complex; contains PCNA-interacting motif | Essential for PCNA unloading, genome stability, and telomere length regulation [1, 4] |
| RFC2 (S. cerevisiae) | Small subunit shared with canonical RFC | Required for complex assembly and ATPase activity [4, 6] |
| RFC3 (S. cerevisiae) | Small subunit shared with canonical RFC | Required for complex assembly and ATPase activity [4, 6] |
| RFC4 (S. cerevisiae) | Small subunit shared with canonical RFC | Required for complex assembly and ATPase activity [4, 6] |
| RFC5 (S. cerevisiae) | Small subunit shared with canonical RFC | Required for complex assembly and ATPase activity [4, 6] |
| ATAD5 (human) | Human homolog of Elg1; large subunit of ATAD5 RFC-like complex | Major PCNA unloader in vertebrates; frequently downregulated in cancers [3, 8] |
| RFC2 (human) | Small subunit of ATAD5 RFC-like complex | Required for ATAD5 complex function [3, 8] |
| RFC3 (human) | Small subunit of ATAD5 RFC-like complex | Required for ATAD5 complex function [3, 8] |
| RFC4 (human) | Small subunit of ATAD5 RFC-like complex | Required for ATAD5 complex function [3, 8] |
| RFC5 (human) | Small subunit of ATAD5 RFC-like complex | Required for ATAD5 complex function [3, 8] |
| PCNA (S. cerevisiae) | Substrate of Elg1-RFC; sliding clamp for DNA polymerase | Unloading target; central to replication and repair [1, 4] |
| PCNA (human) | Substrate of ATAD5-RFC; sliding clamp for DNA polymerase | Unloading target; central to replication and repair [3, 8] |
| RAD53 (S. cerevisiae) | Checkpoint kinase activated by Elg1-RFC in response to DNA damage | Required for DNA damage checkpoint [2, 7] |
| MEC1 (S. cerevisiae) | Checkpoint kinase upstream of Rad53 | Regulates Elg1 induction upon DNA damage |
| CTF18 (S. cerevisiae) | Alternative RFC-like complex subunit | Contrasting roles with Elg1-RFC in genome stability |
| ELG1 (S. pombe) | Fission yeast homolog of Elg1 | Contrasting effects with Ctf18-RFC in absence of functional RFC |
How Is Elg1 RFC-like complex Regulated?
The Elg1 RFC-like complex is regulated primarily at the level of gene expression and protein stability in response to DNA damage and replication stress. In Saccharomyces cerevisiae, ELG1 transcription is induced by DNA-damaging agents such as methyl methanesulfonate (MMS) and hydroxyurea, and this induction requires the checkpoint kinases Mec1 and Rad53. Additionally, the human ATAD5 protein is regulated by ubiquitination and its degradation is linked to the DNA damage response. The complex's activity may also be modulated by post-translational modifications of its subunits, although specific modifications are not fully characterized. Overall, regulation ensures that PCNA unloading is temporally and spatially coupled to replication and repair processes.
Elg1 RFC-like complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ATAD5 (human) | Cancer (breast, ovarian, prostate); genomic instability | ATAD5 knockout cancer cell lines; xenograft models |
| ELG1 (S. cerevisiae) | Genome instability; telomere length dysregulation | Yeast ELG1 deletion strains; telomere length assays [1, 4] |
| PCNA (human) | Cancer; replication stress | PCNA point mutants; PCNA unloading assays [3, 8] |
| RFC2-5 (human) | Cancer; genome instability | Knockout cell lines; complementation assays [3, 8] |
| RAD53 (S. cerevisiae) | DNA damage checkpoint defects | Yeast rad53 mutants; checkpoint activation assays [2, 7] |
Elg1 RFC-like complex and Cancer
The human homolog of Elg1, ATAD5, is frequently downregulated in various cancers, including breast, ovarian, and prostate cancers. Loss of ATAD5 leads to genomic instability, a hallmark of cancer, and may contribute to tumorigenesis by promoting chromosomal rearrangements and mutations. Additionally, mutations in ATAD5 have been associated with increased cancer susceptibility in genome-wide association studies. Targeting the PCNA unloading pathway may therefore offer a therapeutic strategy for cancers with ATAD5 deficiency.
Elg1 RFC-like complex and Genome Instability Syndromes
Defects in PCNA unloading by Elg1-RFC result in genome instability, which is a common feature of premature aging disorders and developmental abnormalities [1, 8]. In yeast, deletion of ELG1 leads to increased recombination, chromosome loss, and sensitivity to DNA-damaging agents [1, 4]. In humans, impaired ATAD5 function may contribute to diseases characterized by genomic instability, although specific syndromes have not been definitively linked. Further research is needed to establish causal relationships between Elg1-RFC dysfunction and human genetic disorders.
Elg1 RFC-like complex and Telomere Maintenance
The Elg1 RFC-like complex plays a role in telomere length regulation, as its deletion in yeast leads to abnormal telomere elongation. Telomere dysfunction is associated with aging and cancer, and understanding how Elg1-RFC regulates telomere length may provide insights into these processes. However, the precise molecular mechanism by which Elg1-RFC affects telomeres remains to be fully elucidated.
From Elg1 RFC-like complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of Elg1 loss on PCNA unloading? | ELG1 knockout yeast or human cells; PCNA chromatin fractionation [1, 4] |
| How does Elg1-RFC contribute to DNA damage checkpoint activation? | ELG1 knockout yeast; Rad53 phosphorylation assays [2, 7] |
| What is the role of Elg1-RFC in telomere length regulation? | ELG1 deletion yeast; telomere Southern blot |
| How does ATAD5 mutation affect cancer cell proliferation? | ATAD5 knockout cancer cell lines; proliferation and xenograft assays |
| What are the structural requirements for PCNA unloading? | Point mutations in ELG1 PIP motif; in vitro unloading assays [4, 8] |
| Can overexpression of Elg1 rescue genome instability? | ELG1 overexpression plasmids in yeast; survival assays [1, 4] |
How to Study the Elg1 RFC-like complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Chromatin fractionation | Amount of PCNA bound to chromatin | Assessing PCNA unloading efficiency [1, 4] |
| DNA damage sensitivity assay | Cell survival upon DNA-damaging agents | Phenotypic characterization of ELG1 mutants [4, 5] |
| Checkpoint activation assay | Phosphorylation of Rad53/CHK1 | Measuring DNA damage checkpoint activation [2, 7] |
| Telomere length analysis | Length of telomeric DNA | Studying telomere regulation by Elg1-RFC |
| Co-immunoprecipitation | Protein-protein interactions | Identifying complex subunits and interactors [4, 6] |
| ATPase assay | ATP hydrolysis activity | Measuring catalytic activity of Elg1-RFC |
| In vitro PCNA unloading assay | Release of PCNA from DNA | Reconstituting unloading with purified components [3, 8] |
| RNA-seq | Transcriptional changes | Identifying genes regulated by Elg1-RFC |
Chromatin Fractionation and PCNA Unloading Assays
Chromatin fractionation followed by immunoblotting for PCNA is a standard method to assess Elg1-RFC activity. Cells are lysed and separated into soluble and chromatin-bound fractions, and the amount of PCNA on chromatin is quantified [1, 4]. This assay can be performed in yeast or human cells and is used to determine the efficiency of PCNA unloading in wild-type versus Elg1 mutant cells [1, 4].
DNA Damage Sensitivity Assays
Sensitivity to DNA-damaging agents such as methyl methanesulfonate (MMS), hydroxyurea, or ultraviolet radiation is a common phenotypic readout for Elg1-RFC function. Spot assays or liquid growth assays are used to compare survival of wild-type and ELG1 mutant strains [4, 5]. These assays are simple and quantitative, and they can be adapted for high-throughput screening.
Checkpoint Activation Assays
The DNA damage checkpoint can be monitored by assessing phosphorylation of Rad53 in yeast or CHK1 in human cells. Elg1-RFC is required for efficient checkpoint activation, so ELG1 mutants show reduced Rad53 phosphorylation upon DNA damage [2, 7]. Western blotting with phospho-specific antibodies is typically used [2, 7].
Telomere Length Analysis
Telomere length is measured by Southern blot of terminal restriction fragments or by quantitative PCR. Deletion of ELG1 leads to telomere elongation defects, making this assay useful for studying the role of Elg1-RFC in telomere maintenance.
How CRISPR Can Be Used to Study GO:0031391 Elg1 RFC-like complex
Knockout
CRISPR-Cas9 knockout of ELG1 or ATAD5 is used to study loss-of-function phenotypes, including PCNA unloading defects, genome instability, and DNA damage sensitivity [1, 4]. Knockout cell lines can be generated in yeast or human cells and are valuable for dissecting the role of Elg1-RFC in replication and repair [1, 4].
Point Mutation
Point mutations in the PCNA-interacting motif (PIP) of ELG1 or in the ATPase domain can be introduced using CRISPR-based base editing or homology-directed repair. These mutants help define the structural requirements for PCNA unloading and ATP hydrolysis [4, 8].
Knock-in
Knock-in of epitope tags (e.g., GFP, HA) into the endogenous ELG1 locus allows for visualization and immunoprecipitation of the complex. This approach is useful for studying complex assembly, localization, and dynamics in live cells [4, 6].
Overexpression
CRISPR activation (CRISPRa) or plasmid-based overexpression of ELG1 can be used to test whether increased PCNA unloading affects replication, repair, or telomere length. Overexpression models are valuable for gain-of-function studies and for testing rescue of phenotypes [1, 4].
How EDITGENE Supports Elg1 RFC-like complex Research
Researchers studying Elg1 RFC-like complex-related genes often need to determine whether a candidate gene is causally involved in PCNA unloading, genome stability, or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research, from knockout and point mutation to knock-in and overexpression models, as well as library screening and bioinformatics support.
Contact EDITGENE today to design your custom CRISPR model for Elg1 RFC-like complex research.
Frequently Asked Questions About Elg1 RFC-like complex
What is the Elg1 RFC-like complex?
The Elg1 RFC-like complex is a pentameric protein complex that unloads PCNA from chromatin and maintains genome stability [1, 4, 6].
What genes are involved in the Elg1 RFC-like complex?
In yeast, the complex includes ELG1, RFC2, RFC3, RFC4, and RFC5. In humans, the homolog is ATAD5 with RFC2-5 [4, 6, 8].
What is the function of Elg1 in DNA replication?
Elg1 unloads PCNA from DNA after replication, preventing aberrant recombination and ensuring proper termination [1, 4].
How is the Elg1 RFC-like complex related to cancer?
The human homolog ATAD5 is frequently downregulated in cancers, and its loss leads to genomic instability.
What diseases are associated with Elg1 RFC-like complex dysfunction?
Dysfunction is linked to cancer and genome instability syndromes, though specific diseases are still being investigated.
What are the subunits of the Elg1 RFC-like complex?
The complex consists of Elg1p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p in Saccharomyces cerevisiae [4, 6].
How does Elg1 RFC-like complex differ from canonical RFC?
Elg1-RFC unloads PCNA, while canonical RFC loads PCNA onto DNA during replication [1, 8].
What research methods are used to study Elg1 RFC-like complex?
Common methods include chromatin fractionation, DNA damage sensitivity assays, checkpoint activation assays, and telomere length analysis [1, 2, 4].
Can CRISPR be used to study Elg1 RFC-like complex?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to dissect Elg1-RFC function [1, 4].
What is the role of Elg1 in telomere length regulation?
Elg1-RFC is involved in telomere length regulation, as its deletion leads to abnormal telomere elongation.
Conclusion
The Elg1 RFC-like complex (GO:0031391) is a critical PCNA unloader that safeguards genome stability, regulates telomere length, and activates the DNA damage checkpoint. Its human homolog ATAD5 is frequently dysregulated in cancer, highlighting its clinical relevance. Continued research using CRISPR-based models and advanced screening technologies will further elucidate its mechanisms and therapeutic potential.
References
- 1. Aroya SB et al.. 2005. The Elg1 replication factor C-like complex: a novel guardian of genome stability.. DNA Repair (Amst) 4(4):409-17 PMID: 15725622
- 2. Sau S et al.. 2019. The Yeast PCNA Unloader Elg1 RFC-Like Complex Plays a Role in Eliciting the DNA Damage Checkpoint.. mBio 10(3) PMID: 31186330
- 3. Kawasoe Y et al.. 2024. The Atad5 RFC-like complex is the major unloader of proliferating cell nuclear antigen in Xenopus egg extracts.. J Biol Chem 300(1):105588 PMID: 38141767
- 4. Kanellis P et al.. 2003. Elg1 forms an alternative PCNA-interacting RFC complex required to maintain genome stability.. Curr Biol 13(18):1583-95 PMID: 13678589
- 5. Kim J et al.. 2005. Contrasting effects of Elg1-RFC and Ctf18-RFC inactivation in the absence of fully functional RFC in fission yeast.. Nucleic Acids Res 33(13):4078-89 PMID: 16040599
- 6. Ben-Aroya S et al.. 2003. ELG1, a yeast gene required for genome stability, forms a complex related to replication factor C.. Proc Natl Acad Sci U S A 100(17):9906-11 PMID: 12909721
- 7. Sau S et al.. 2020. A role for the yeast PCNA unloader Elg1 in eliciting the DNA damage checkpoint.. Curr Genet 66(1):79-84 PMID: 31332476
- 8. Lee KY et al.. 2020. Eukaryotic clamp loaders and unloaders in the maintenance of genome stability.. Exp Mol Med 52(12):1948-1958 PMID: 33339954
