Affinage

RNASEH1

Ribonuclease H1 · UniProt O60930

Length
286 aa
Mass
32.1 kDa
Annotated
2026-06-10
20 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

RNASEH1 encodes an endonuclease that recognizes and cleaves the RNA strand of RNA:DNA hybrids through its catalytic domain, a specificity exploited to map R-loops genome-wide using a catalytically dead mutant that binds without resolving hybrids (PMID:30996261). A fraction of the predominantly nuclear enzyme is targeted to mitochondria, where it is essential for mitochondrial DNA replication; its loss causes mtDNA depletion and embryonic lethality in mice, and conditional knockouts in liver and B cells reproduce the mtDNA replication defect [PMID:12667461, PMID:27131367, PMID:bio_10.1101_2025.04.30.651504]. Consistent with this essential mitochondrial role, pathogenic human mutations that abolish RNase H activity cause accumulation of multiple mtDNA deletions and adult-onset mitochondrial encephalomyopathy (PMID:26094573, PMID:31258551). In the nucleus, RNaseH1 recruitment to R-loops is driven by a direct interaction with RPA, which enhances hybrid binding and stimulates cleavage; an RPA-binding-defective mutant fails to localize to R-loops and to suppress R-loop-associated genomic instability (PMID:28257700). Its endonucleolytic activity is further coupled to the 3'-5' exonuclease REXO4 in an endo/exo-cleavage mechanism that degrades R-loops (PMID:41706852). At ALT telomeres, RNaseH1 resolves TERRA-telomeric RNA:DNA hybrids to restrain recombination-based telomere maintenance, with depletion driving hybrid accumulation and telomere excision and overexpression reducing telomere recombinogenicity (PMID:25330849). Oxidative stress restricts RNaseH1 function in mitochondria by causing 8-oxoguanine accumulation in mtDNA that impairs its recruitment to R-loops in the regulatory region, thereby limiting replication initiation (PMID:34348152).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2003 High

    Established that RNase H1, though predominantly nuclear, has an essential and non-redundant role in mitochondrial DNA replication, resolving whether the enzyme was merely a nuclear hybrid nuclease.

    Evidence Rnaseh1 null mouse with subcellular fractionation and mtDNA quantification

    PMID:12667461

    Open questions at the time
    • Did not define the molecular substrate in mitochondria (RNA primer removal vs other hybrids)
    • Did not address nuclear function in adult tissues
  2. 2014 High

    Showed RNaseH1 controls telomeric RNA:DNA hybrids between TERRA and telomeric DNA, linking hybrid resolution to recombination-based telomere maintenance in ALT cancer cells.

    Evidence Knockdown/overexpression with telomeric ChIP, immunofluorescence, and DRIP in ALT cells

    PMID:25330849

    Open questions at the time
    • Recruitment mechanism to telomeres not defined
    • Whether this reflects a general nuclear role or an ALT-specific dependency unclear
  3. 2015 High

    Connected loss of RNase H1 catalytic activity directly to human disease, establishing it as a cause of adult-onset mitochondrial encephalomyopathy with multiple mtDNA deletions.

    Evidence In vitro hybrid cleavage assay on patient mutations plus sequencing of patient mtDNA

    PMID:26094573

    Open questions at the time
    • Did not resolve the precise replication step disrupted
    • Genotype-phenotype relationship across mutations not fully mapped
  4. 2016 High

    Confirmed the mitochondrial requirement in adult tissue and demonstrated RNase H1 is needed for both R-loop processing and the in vivo activity of DNA-like antisense oligonucleotides.

    Evidence Liver-specific and inducible Rnaseh1 knockout mice with R-loop and mitochondrial functional readouts

    PMID:27131367

    Open questions at the time
    • Did not separate nuclear R-loop contribution from mitochondrial dysfunction in the phenotype
    • Did not define which R-loops are direct substrates
  5. 2017 High

    Identified RPA as the direct partner that recruits and activates RNaseH1 at nuclear R-loops, explaining how the enzyme is targeted to hybrids to protect genome stability.

    Evidence Co-IP, in vitro reconstitution with purified RPA and RNaseH1, interface mutagenesis, and cellular R-loop imaging

    PMID:28257700

    Open questions at the time
    • Whether RPA recruitment operates at telomeres and mitochondria not addressed
    • Other recruitment factors not excluded
  6. 2019 Medium

    Demonstrated that the catalytic domain itself confers RNA:DNA hybrid recognition, enabling a catalytically dead enzyme to be used as a genome-wide R-loop mapping tool.

    Evidence Catalytically inactive RNASEH1 mutant in R-ChIP with strand-specific ChIP-seq

    PMID:30996261

    Open questions at the time
    • Mapping reflects mutant binding, which may not match endogenous turnover
    • Single lab
  7. 2019 Medium

    Extended the disease mutation spectrum to the connection domain, showing both catalytic and connection-domain mutations impair mtDNA replication recovery.

    Evidence In vitro RNase H assay and mtDNA copy number recovery in patient fibroblasts

    PMID:31258551

    Open questions at the time
    • Single patient study
    • Mechanism by which connection-domain mutation impairs activity not biochemically dissected
  8. 2021 Medium

    Revealed that oxidative damage to mtDNA (8-oxoguanine) impairs RNaseH1 recruitment to mitochondrial R-loops, linking ROS and BRCA2 status to restricted mtDNA replication initiation.

    Evidence Mitochondrial R-loop imaging, RNaseH1 localization, ROS and BRCA2 manipulation, replication initiation assays

    PMID:34348152

    Open questions at the time
    • Molecular basis of how 8-oxoguanine blocks recruitment not defined
    • Single lab
  9. 2022 Medium

    Defined an endo/exo-cleavage coupling whereby REXO4 exonuclease collaborates with and stimulates RNaseH1 to degrade R-loops genome-wide.

    Evidence In vitro cleavage assays, co-IP, R-ChIP, and REXO4 overexpression in RNaseH1-deficient cells

    PMID:41706852

    Open questions at the time
    • Physiological contexts requiring the coupling not mapped
    • Single lab
  10. 2025 Medium

    Challenged the assumption that RNaseH1 broadly resolves co-transcriptional R-loops, showing its essential function in B cells is mitochondrial rather than nuclear R-loop control.

    Evidence Conditional knockout and overexpression in primary B cells with genome-wide R-loop mapping (preprint)

    PMID:bio_10.1101_2025.04.30.651504

    Open questions at the time
    • Preprint, not yet peer-reviewed
    • Reconciliation with R-loop suppression seen in other cell types unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unclear how the balance between RNaseH1's essential mitochondrial role and its context-dependent nuclear/telomeric R-loop functions is regulated, and which R-loops it directly acts upon in vivo.
  • Direct in vivo nuclear substrates not defined
  • Mechanism partitioning the enzyme between compartments unknown
  • Telomeric and RPA-dependent recruitment not integrated with mitochondrial recruitment

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140098 catalytic activity, acting on RNA 3 GO:0003723 RNA binding 1
Localization
GO:0005739 mitochondrion 3 GO:0005634 nucleus 2
Partners
REXO4RPA

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 RNase H1 is required for mitochondrial DNA replication; a fraction of the predominantly nuclear RNase H1 is targeted to mitochondria, and its absence causes a significant decrease in mitochondrial DNA content leading to embryonic lethality at E8.5 in mice, providing direct support for the strand-coupled mechanism of mitochondrial DNA replication. Rnaseh1 null mouse generation, subcellular fractionation, mitochondrial DNA quantification, apoptosis assays Molecular Cell High 12667461
2014 RNaseH1 associates specifically with telomeres in ALT (Alternative Lengthening of Telomeres) cancer cells and regulates levels of RNA-DNA hybrids between telomeric DNA and the lncRNA TERRA; its depletion causes telomeric hybrid accumulation, single-stranded telomeric DNA exposure, RPA activation at telomeres, and abrupt telomere excision, while its overexpression reduces ALT telomere recombinogenicity and leads to telomere shortening. RNaseH1 knockdown/overexpression, chromatin immunoprecipitation at telomeres, immunofluorescence, DNA-RNA immunoprecipitation (DRIP) Nature Communications High 25330849
2015 Pathogenic mutations in RNASEH1 impair the enzyme's ability to remove RNA from RNA-DNA hybrids (demonstrated by in vitro RNase H activity assay), leading to reduced mtDNA replication, accumulation of multiple mtDNA deletions, and adult-onset mitochondrial encephalomyopathy in humans. In vitro RNA-DNA hybrid cleavage assay with mutant RNase H1, Western blot, next-generation sequencing of patient samples American Journal of Human Genetics High 26094573
2016 RNase H1 is required for processing R-loops and for mitochondrial genome maintenance in hepatocytes; liver-specific knockout increases R-loop levels, reduces mitochondrial-encoded DNA and mRNA, and causes mitochondrial dysfunction, apoptosis, and fibrosis. Additionally, RNase H1 is necessary for the activity of DNA-like antisense oligonucleotides (ASOs) in vivo. Conditional liver-specific and tamoxifen-inducible Rnaseh1 knockout mice, R-loop quantification, mitochondrial morphology/function assays, ASO activity assays Nucleic Acids Research High 27131367
2017 Replication protein A (RPA) directly interacts with RNaseH1, colocalizes with RNaseH1 and R-loops in cells, enhances RNaseH1 association with RNA:DNA hybrids in vitro, and stimulates RNaseH1 activity on R-loops. An RPA-binding-defective RNaseH1 mutant fails to accumulate at R-loops in cells and loses the ability to suppress R-loop-associated genomic instability. Co-immunoprecipitation, in vitro biochemical assay with purified RPA and RNaseH1, site-directed mutagenesis of RNaseH1 RPA-binding interface, cellular R-loop immunofluorescence Molecular Cell High 28257700
2019 A catalytically inactive mutant of RNASEH1 binds RNA-DNA hybrids without resolving them, enabling R-ChIP, a genome-wide chromatin immunoprecipitation method for mapping R-loops; this established that RNASEH1 specifically recognizes RNA:DNA hybrid structures via its catalytic domain. Catalytically inactive RNASEH1 mutant expression, ChIP-seq, strand-specific library sequencing Nature Protocols Medium 30996261
2019 Two novel homozygous RNASEH1 mutations (c.487T>C in the catalytic domain and c.258_260del in the connection domain) both cause loss of ribonuclease H1 activity and impair mtDNA replication, as shown by inability to recover normal mtDNA copy number after ethidium bromide-induced depletion in patient fibroblasts. In vitro RNase H activity assay, mtDNA copy number recovery assay in patient fibroblasts, in silico structural modeling Frontiers in Genetics Medium 31258551
2021 Oxidative stress causes 8-oxoguanine accumulation in mtDNA, which impairs recruitment of RNaseH1 to sites of R-loop accrual in the mtDNA regulatory region, thereby restricting mtDNA replication initiation. BRCA2 inactivation elevates ROS, phenocopying this defect, and ROS scavengers suppress the mtDNA replication defects. R-loop immunofluorescence in mitochondria, RNaseH1 localization assays, ROS manipulation (pharmacologic and genetic), BRCA2 knockdown/knockout, mtDNA replication initiation assays Cell Reports Medium 34348152
2022 REXO4 (a 3'-5' exonuclease) collaborates with RNaseH1 endonuclease to degrade R-loops in an 'endo/exo-cleavage coupling' manner; REXO4 directly stimulates RNaseH1 endonuclease activity, and REXO4 overexpression counteracts genome-wide R-loop accumulation caused by RNaseH1 deficiency. In vitro cleavage assays, co-immunoprecipitation, genome-wide R-loop mapping (R-ChIP), REXO4 overexpression in RNaseH1-deficient cells Science Advances Medium 41706852
2025 Conditional knockout of Rnaseh1 in primary murine B cells causes dramatic loss of mitochondrial DNA replication and compromised B cell responses, but does not significantly affect genome-wide nuclear R-loop levels. Conversely, overexpression of active nuclear RNaseH1 does not reduce nuclear R-loop levels, indicating that co-transcriptional R-loops are not efficiently resolved by RNaseH1. Conditional Rnaseh1 knockout and overexpression in primary B cells, genome-wide R-loop mapping, mitochondrial DNA quantification, B cell functional assays bioRxivpreprint Medium bio_10.1101_2025.04.30.651504

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2014 RNaseH1 regulates TERRA-telomeric DNA hybrids and telomere maintenance in ALT tumour cells. Nature communications 392 25330849
2003 Failure to produce mitochondrial DNA results in embryonic lethality in Rnaseh1 null mice. Molecular cell 284 12667461
2017 Functions of Replication Protein A as a Sensor of R Loops and a Regulator of RNaseH1. Molecular cell 228 28257700
2015 RNASEH1 Mutations Impair mtDNA Replication and Cause Adult-Onset Mitochondrial Encephalomyopathy. American journal of human genetics 87 26094573
2016 Viable RNaseH1 knockout mice show RNaseH1 is essential for R loop processing, mitochondrial and liver function. Nucleic acids research 82 27131367
2019 R-ChIP for genome-wide mapping of R-loops by using catalytically inactive RNASEH1. Nature protocols 61 30996261
2021 BRCA2 deficiency reveals that oxidative stress impairs RNaseH1 function to cripple mitochondrial DNA maintenance. Cell reports 29 34348152
2017 Clinicopathologic and molecular spectrum of RNASEH1-related mitochondrial disease. Neurology. Genetics 23 28508084
2022 The Combination of Mesyl-Phosphoramidate Inter-Nucleotide Linkages and 2'-O-Methyl in Selected Positions in the Antisense Oligonucleotide Enhances the Performance of RNaseH1 Active PS-ASOs. Nucleic acid therapeutics 22 35861704
2022 Long noncoding RNASEH1-AS1 exacerbates the progression of non-small cell lung cancer by acting as a ceRNA to regulate microRNA-516a-5p/FOXK1 and thereby activating the Wnt/β-catenin signaling pathway. Cancer medicine 11 35166053
2019 Identification and Characterization of New RNASEH1 Mutations Associated With PEO Syndrome and Multiple Mitochondrial DNA Deletions. Frontiers in genetics 10 31258551
2023 A pan-cancer analysis of RNASEH1, a potential regulator of the tumor microenvironment. Clinical & translational oncology : official publication of the Federation of Spanish Oncology Societies and of the National Cancer Institute of Mexico 6 37022517
2024 uORF-targeting steric block antisense oligonucleotides do not reproducibly increase RNASEH1 expression. Molecular therapy. Nucleic acids 5 39759875
2022 Case Report: Rare Homozygous RNASEH1 Mutations Associated With Adult-Onset Mitochondrial Encephalomyopathy and Multiple Mitochondrial DNA Deletions. Frontiers in genetics 5 35711919
2017 RNASEH1 gene variants are associated with autoimmune type 1 diabetes in Colombia. Journal of endocrinological investigation 4 29204916
2022 Mapping R-Loops Using Catalytically Inactive RNaseH1 (R-ChIP). Methods in molecular biology (Clifton, N.J.) 2 35704204
2022 Protocol to use RNaseH1-based CRISPR to modulate locus-associated R-loops. STAR protocols 1 36178790
2026 R-loop processing via REXO4-RNaseH1-mediated endo- and exo-cleavage coupling mode prevents genome instability and antitumor immunity. Science advances 0 41706852
2023 RNASEH1-AS1 induced by H3K27ac stabilizes ANXA2 mRNA to promote the progression of colorectal cancer through recruiting BUD13. Neoplasma 0 38053379
2020 A non-coding RNASEH1 gene variant associates with type 1 diabetes and interacts with HLA tagSNPs in families from Colombia. Pediatric diabetes 0 32447804

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