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Nitiss KC, Bandak A, Berger JM, Nitiss JL. Genome Instability Induced by Topoisomerase Misfunction. Int J Mol Sci 2024; 25:10247. [PMID: 39408578 PMCID: PMC11477040 DOI: 10.3390/ijms251910247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2024] [Revised: 09/19/2024] [Accepted: 09/20/2024] [Indexed: 10/20/2024] Open
Abstract
Topoisomerases alter DNA topology by making transient DNA strand breaks (DSBs) in DNA. The DNA cleavage reaction mechanism includes the formation of a reversible protein/DNA complex that allows rapid resealing of the transient break. This mechanism allows changes in DNA topology with minimal risks of persistent DNA damage. Nonetheless, small molecules, alternate DNA structures, or mutations in topoisomerase proteins can impede the resealing of the transient breaks, leading to genome instability and potentially cell death. The consequences of high levels of enzyme/DNA adducts differ for type I and type II topoisomerases. Top1 action on DNA containing ribonucleotides leads to 2-5 nucleotide deletions in repeated sequences, while mutant Top1 enzymes can generate large deletions. By contrast, small molecules that target Top2, or mutant Top2 enzymes with elevated levels of cleavage lead to small de novo duplications. Both Top1 and Top2 have the potential to generate large rearrangements and translocations. Thus, genome instability due to topoisomerase mis-function is a potential pathogenic mechanism especially leading to oncogenic progression. Recent studies support the potential roles of topoisomerases in genetic changes in cancer cells, highlighting the need to understand how cells limit genome instability induced by topoisomerases. This review highlights recent studies that bear on these questions.
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Affiliation(s)
- Karin C. Nitiss
- Pharmaceutical Sciences Department, University of Illinois Chicago, Rockford, IL 61107, USA;
| | - Afif Bandak
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 20215, USA; (A.B.); (J.M.B.)
| | - James M. Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 20215, USA; (A.B.); (J.M.B.)
| | - John L. Nitiss
- Pharmaceutical Sciences Department, University of Illinois Chicago, Rockford, IL 61107, USA;
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2
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Anticevic I, Otten C, Popovic M. Tyrosyl-DNA phosphodiesterase 2 (Tdp2) repairs DNA-protein crosslinks and protects against double strand breaks in vivo. Front Cell Dev Biol 2024; 12:1394531. [PMID: 39228401 PMCID: PMC11369425 DOI: 10.3389/fcell.2024.1394531] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 06/06/2024] [Indexed: 09/05/2024] Open
Abstract
DNA-protein crosslinks pose a significant challenge to genome stability and cell viability. Efficient repair of DPCs is crucial for preserving genomic integrity and preventing the accumulation of DNA damage. Despite recent advances in our understanding of DPC repair, many aspects of this process, especially at the organismal level, remain elusive. In this study, we used zebrafish as a model organism to investigate the role of TDP2 (Tyrosyl-DNA phosphodiesterase 2) in DPC repair. We characterized the two tdp2 orthologs in zebrafish using phylogenetic, syntenic and expression analysis and investigated the phenotypic consequences of tdp2 silencing in zebrafish embryos. We then quantified the effects of tdp2a and tdp2b silencing on cellular DPC levels and DSB accumulation in zebrafish embryos. Our findings revealed that tdp2b is the main ortholog during embryonic development, while both orthologs are ubiquitously present in adult tissues. Notably, the tdp2b ortholog is phylogenetically closer to human TDP2. Silencing of tdp2b, but not tdp2a, resulted in the loss of Tdp2 activity in zebrafish embryos, accompanied by the accumulation of DPCs and DSBs. Our findings contribute to a more comprehensive understanding of DPC repair at the organismal level and underscore the significance of TDP2 in maintaining genome stability.
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Affiliation(s)
| | | | - Marta Popovic
- DNA Damage Group, Laboratory for Molecular Ecotoxicology, Department for Marine and Environmental Research, Institute Ruder Boskovic, Zagreb, Croatia
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Salih MA. The Meryon Lecture at the 24th annual meeting of the Meryon Society, St. Anne's College, Oxford, UK, 15th July 2022: Neuromuscular diseases in the Arab population. Neuromuscul Disord 2023; 33:792-799. [PMID: 37679229 DOI: 10.1016/j.nmd.2023.08.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/09/2023]
Affiliation(s)
- Mustafa A Salih
- Consultant Pediatric Neurologist, Health Sector, King Abdulaziz City for Science and Technology, Riyadh 11442, Saudi Arabia.
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Brettrager EJ, Cuya SM, Tibbs ZE, Zhang J, Falany CN, Aller SG, van Waardenburg RCAM. N-terminal domain of tyrosyl-DNA phosphodiesterase I regulates topoisomerase I-induced toxicity in cells. Sci Rep 2023; 13:1377. [PMID: 36697463 PMCID: PMC9876888 DOI: 10.1038/s41598-023-28564-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 01/20/2023] [Indexed: 01/27/2023] Open
Abstract
Tyrosyl-DNA phosphodiesterase I (Tdp1) hydrolyzes phosphodiester-linked adducts from both ends of DNA. This includes the topoisomerase I (TOP1)-DNA covalent reaction intermediate that is the target of the camptothecin class of chemotherapeutics. Tdp1 two-step catalysis is centered on the formation of a Tdp1-DNA covalent complex (Tdp1cc) using two catalytic histidines. Here, we examined the role of the understudied, structurally undefined, and poorly conserved N-terminal domain (NTD) of Tdp1 in context of full-length protein in its ability to remove TOP1cc in cells. Using toxic Tdp1 mutants, we observed that the NTD is critical for Tdp1's ability to remove TOP1-DNA adducts in yeast. Full-length and N-terminal truncated Tdp1 mutants showed similar expression levels and cellular distribution yet an inversed TOP1-dependent toxicity. Single turnover catalysis was significantly different between full-length and truncated catalytic mutants but not wild-type enzyme, suggesting that Tdp1 mutants depend on the NTD for catalysis. These observations suggest that the NTD plays a critical role in the regulation of Tdp1 activity and interaction with protein-DNA adducts such as TOP1cc in cells. We propose that the NTD is a regulatory domain and coordinates stabilization of the DNA-adducted end within the catalytic pocket to access the phosphodiester linkage for hydrolysis.
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Affiliation(s)
- Evan J Brettrager
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA
| | - Selma M Cuya
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA.,Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, GA, 30144, USA
| | - Zachary E Tibbs
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA.,Cardiothoracic Surgery - Ascension Medical Group, 10580 North Meridian St. Ste 105, Carmel, IN, 46290, USA
| | - Jun Zhang
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
| | - Charles N Falany
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA
| | - Stephen G Aller
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA
| | - Robert C A M van Waardenburg
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 155 Volker Hall, 1720 2nd Ave S., Birmingham, AL, 35294, USA.
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Caldecott KW. DNA single-strand break repair and human genetic disease. Trends Cell Biol 2022; 32:733-745. [PMID: 35643889 DOI: 10.1016/j.tcb.2022.04.010] [Citation(s) in RCA: 61] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2021] [Revised: 04/13/2022] [Accepted: 04/22/2022] [Indexed: 12/15/2022]
Abstract
DNA single-strand breaks (SSBs) are amongst the commonest DNA lesions arising in cells, with many tens of thousands induced in each cell each day. SSBs arise not only from exposure to intracellular and environmental genotoxins but also as intermediates of normal DNA metabolic processes, such as the removal of torsional stress in DNA by topoisomerase enzymes and the epigenetic regulation of gene expression by DNA base excision repair (BER). If not rapidly detected and repaired, SSBs can result in RNA polymerase stalling, DNA replication fork collapse, and hyperactivation of the SSB sensor protein poly(ADP-ribose) polymerase 1 (PARP1). The potential impact of unrepaired SSBs is illustrated by the existence of genetic diseases in which proteins involved in SSB repair (SSBR) are mutated, and which are typified by hereditary neurodevelopmental and/or neurodegenerative disease. Here, I review our current understanding of SSBR and its impact on human neurological disease, with a focus on recent developments and concepts.
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Affiliation(s)
- Keith W Caldecott
- Genome Damage and Stability Centre, School of Life Sciences, Science Park Road, University of Sussex, Falmer, Brighton BN1 9RQ, UK.
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Dragašević-Mišković N, Stanković I, Milovanović A, Kostić VS. Autosomal recessive adult onset ataxia. J Neurol 2021; 269:504-533. [PMID: 34499204 DOI: 10.1007/s00415-021-10763-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 08/16/2021] [Accepted: 08/18/2021] [Indexed: 11/24/2022]
Abstract
Autosomal recessive ataxias (ARCA) represent a complex group of diseases ranging from primary ataxias to rare and complex metabolic disorders in which ataxia is a part of the clinical picture. Small number of ARCA manifest exclusively in adulthood, while majority of typical childhood onset ARCA may also start later with atypical clinical presentation. We have systematically searched the literature for ARCA with adult onset, both in the group of primary ataxias including those that are less frequently described in isolated or in a small number of families, and also in the group of complex and metabolic diseases in which ataxia is only part of the clinical picture. We propose an algorithm that could be used when encountering a patient with adult onset sporadic or recessive ataxia in whom the acquired causes are excluded. ARCA are frequently neglected in the differential diagnosis of adult-onset ataxias. Rising awareness of their clinical significance is important, not only because some of these disorders may be potentially treatable, but also for prognostic implications and inclusion of patients to future clinical trials with disease modifying agents.
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Affiliation(s)
- Nataša Dragašević-Mišković
- Neurology Clinic, Clinical Center of Serbia, School of Medicine, University of Belgrade, Dr Subotića 6, 11000, Belgrade, Serbia.
| | - Iva Stanković
- Neurology Clinic, Clinical Center of Serbia, School of Medicine, University of Belgrade, Dr Subotića 6, 11000, Belgrade, Serbia
| | - Andona Milovanović
- Neurology Clinic, Clinical Center of Serbia, School of Medicine, University of Belgrade, Dr Subotića 6, 11000, Belgrade, Serbia
| | - Vladimir S Kostić
- Neurology Clinic, Clinical Center of Serbia, School of Medicine, University of Belgrade, Dr Subotića 6, 11000, Belgrade, Serbia
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Abstract
Objectives: Generally, neuropathies of peripheral nerves are a frequent condition (prevalence 2–3%) and most frequently due to alcoholism, diabetes, renal insufficiency, malignancy, toxins, or drugs. However, the vast majority of neuropathies has orphan status. This review focuses on the etiology, frequency, diagnosis, and treatment of orphan neuropathies. Methods: Literature review Results: Rareness of diseases is not uniformly defined but in the US an orphan disease is diagnosed if the prevalence is <1:200000, in Europe if <5:10000. Most acquired and hereditary neuropathies are orphan diseases. Often the causative variant has been reported only in a single patient or family, particularly the ones that are newly detected (e.g. SEPT9, SORD). Among the complex neuropathies (hereditary multisystem disorders with concomitant neuropathies) orphan forms have been reported among mitochondrial disorders (e.g. NARP, MNGIE, SANDO), spinocerebellar ataxias (e.g. TMEM240), hereditary spastic paraplegias (e.g UBAP1), lysosomal storage disease (e.g. Schindler disease), peroxisomal disorders, porphyrias, and other types (e.g. giant axonal neuropathy, Tangier disease). Orphan acquired neuropathies include the metabolic neuropathies (e.g. vitamin-B1, folic acid), toxic neuropathies (e.g. copper, lithium, lead, arsenic, thallium, mercury), infectious neuropathies, immune-mediated (e.g. Bruns-Garland syndrome), and neoplastic/paraneoplastic neuropathies. Conclusions: Though orphan neuropathies are rare per definition they constitute the majority of neuropathies and should be considered as some of them are easy to identify and potentially treatable, as clarification of the underlying cause may contribute to the knowledge about etiology and pathophysiology of these conditions, and as the true prevalence may become obvious only if all ever diagnosed cases are reported.
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Affiliation(s)
| | | | - Julia Wanschitz
- Department of Neurology, Medical University, Innsbruck, Austria
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Zagnoli-Vieira G, Caldecott KW. Untangling trapped topoisomerases with tyrosyl-DNA phosphodiesterases. DNA Repair (Amst) 2020; 94:102900. [PMID: 32653827 DOI: 10.1016/j.dnarep.2020.102900] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 06/14/2020] [Accepted: 06/14/2020] [Indexed: 02/08/2023]
Abstract
DNA topoisomerases alleviate the torsional stress that is generated by processes that are central to genome metabolism such as transcription and DNA replication. To do so, these enzymes generate an enzyme intermediate known as the cleavage complex in which the topoisomerase is covalently linked to the termini of a DNA single- or double-strand break. Whilst cleavage complexes are normally transient they can occasionally become abortive, creating protein-linked DNA breaks that threaten genome stability and cell survival; a process promoted and exploited in the cancer clinic by the use of topoisomerase 'poisons'. Here, we review the consequences to genome stability and human health of abortive topoisomerase-induced DNA breakage and the cellular pathways that cells have adopted to mitigate them, with particular focus on an important class of enzymes known as tyrosyl-DNA phosphodiesterases.
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Affiliation(s)
- Guido Zagnoli-Vieira
- Wellcome Trust Cancer Research UK Gurdon Institute, Tennis Court Road, Cambridge, CB2 1QN, UK.
| | - Keith W Caldecott
- Genome Damage Stability Centre, University of Sussex, Falmer Road, Brighton, BN1 9RQ, UK.
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Seidahmed MZ, Hamad MH, AlBakheet A, Elmalik SA, AlDrees A, Al-Sufayan J, Alorainy I, Ghozzi IM, Colak D, Salih MA, Kaya N. Ancient founder mutation in RUBCN: a second unrelated family confirms Salih ataxia (SCAR15). BMC Neurol 2020; 20:207. [PMID: 32450808 PMCID: PMC7249383 DOI: 10.1186/s12883-020-01761-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 05/03/2020] [Indexed: 11/24/2022] Open
Abstract
Background Homozygous frameshift mutation in RUBCN (KIAA0226), known to result in endolysosomal machinery defects, has previously been reported in a single Saudi family with autosomal recessive spinocerebellar ataxia (Salih ataxia, SCAR15, OMIM # 615705). The present report describes the clinical, neurophysiologic, neuroimaging, and genetic findings in a second unrelated Saudi family with two affected children harboring identical homozygous frameshift mutation in the gene. It also explores and documents an ancient founder cerebellar ataxia mutation in the Arabian Peninsula. Case presentation The present family has two affected males (aged 6.5 and 17 years) with unsteady gait apparent since learning to walk at 2.5 and 3 years, respectively. The younger patient showed gait ataxia and normal reflexes. The older patient had saccadic eye movement, dysarthria, mild upper and lower limb and gait ataxia (on tandem walking), and enhanced reflexes in the lower limbs. Cognitive abilities were mildly impaired in the younger sibling (IQ 67) and borderline in the older patient (IQ 72). Nerve conduction studies were normal in both patients. MRI was normal at 2.5 years in the younger sibling. Brain MRI showed normal cerebellar volume and folia in the older sibling at the age of 6 years, and revealed minimal superior vermian atrophy at the age of 16 years. Autozygome and exome analysis showed both affected have previously reported homoallelic mutation in RUBCN (NM_014687:exon18:c.2624delC:p.A875fs), whereas the parents are carriers. Autozygosity mapping focused on smallest haplotype on chromosome 3 and mutation age analysis revealed the mutation occurred approximately 1550 years ago spanning about 62 generations. Conclusions Our findings validate the slowly progressive phenotype of Salih ataxia (SCAR15, OMIM # 615705) by an additional family. Haplotype sharing attests to a common founder, an ancient RUBCN mutation in the Arab population.
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Affiliation(s)
- Mohammed Z Seidahmed
- Neonatology Unit, Department of Pediatrics, Security Forces Hospital, Riyadh, 11481, Saudi Arabia.
| | - Muddathir H Hamad
- Division of Pediatric Neurology, Department of Pediatrics, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Albandary AlBakheet
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, MBC: 03, P.O. Box 3354, Riyadh, 11211, Kingdom of Saudi Arabia
| | - Salah A Elmalik
- Department of Physiology, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Abdulmajeed AlDrees
- Department of Physiology, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Jumanah Al-Sufayan
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, MBC: 03, P.O. Box 3354, Riyadh, 11211, Kingdom of Saudi Arabia
| | - Ibrahim Alorainy
- Department of Radiology and Diagnostic Imaging, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Ibrahim M Ghozzi
- Department of Internal Medicine, Division of Neurology, Security Forces Hospital, Riyadh, Saudi Arabia
| | - Dilek Colak
- Department of Biostatistics, Epidemiology, and Scientific Computing, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Mustafa A Salih
- Division of Pediatric Neurology, Department of Pediatrics, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Namik Kaya
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, MBC: 03, P.O. Box 3354, Riyadh, 11211, Kingdom of Saudi Arabia.
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Brettrager EJ, van Waardenburg RC. Targeting Tyrosyl-DNA phosphodiesterase I to enhance toxicity of phosphodiester linked DNA-adducts. CANCER DRUG RESISTANCE (ALHAMBRA, CALIF.) 2019; 2:1153-1163. [PMID: 31875206 PMCID: PMC6929713 DOI: 10.20517/cdr.2019.91] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Revised: 11/19/2019] [Accepted: 11/29/2019] [Indexed: 06/10/2023]
Abstract
Our genomic DNA is under constant assault from endogenous and exogenous sources, which needs to be resolved to maintain cellular homeostasis. The eukaryotic DNA repair enzyme Tyrosyl-DNA phosphodiesterase I (Tdp1) catalyzes the hydrolysis of phosphodiester bonds that covalently link adducts to DNA-ends. Tdp1 utilizes two catalytic histidines to resolve a growing list of DNA-adducts. These DNA-adducts can be divided into two groups: small adducts, including oxidized nucleotides, RNA, and non-canonical nucleoside analogs, and large adducts, such as (drug-stabilized) topoisomerase- DNA covalent complexes or failed Schiff base reactions as occur between PARP1 and DNA. Many Tdp1 substrates are generated by chemotherapeutics linking Tdp1 to cancer drug resistance, making a compelling argument to develop small molecules that target Tdp1 as potential novel therapeutic agents. Tdp1's unique catalytic cycle, which is centered on the formation of Tdp1-DNA covalent reaction intermediate, allows for two principally different targeting strategies: (1) catalytic inhibition of Tdp1 catalysis to prevent Tdp1-mediated repair of DNA-adducts that enhances the effectivity of chemotherapeutics; and (2) poisoning of Tdp1 by stabilization of the Tdp1- DNA covalent reaction intermediate, which would increase the half-life of a potentially toxic DNA-adduct by preventing its resolution, analogous to topoisomerase targeted poisons such as topotecan or etoposide. The catalytic Tdp1 mutant that forms the molecular basis of the autosomal recessive neurodegenerative disease spinocerebellar ataxia with axonal neuropathy best illustrates this concept; however, no small molecules have been reported for this strategy. Herein, we concisely discuss the development of Tdp1 catalytic inhibitors and their results.
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Affiliation(s)
- Evan J. Brettrager
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL 35294-0019, USA
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Tyrosyl-DNA Phosphodiesterase I N-Terminal Domain Modifications and Interactions Regulate Cellular Function. Genes (Basel) 2019; 10:genes10110897. [PMID: 31698852 PMCID: PMC6895789 DOI: 10.3390/genes10110897] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 10/30/2019] [Accepted: 11/04/2019] [Indexed: 01/09/2023] Open
Abstract
The conserved eukaryotic DNA repair enzyme Tyrosyl-DNA phosphodiesterase I (Tdp1) removes a diverse array of adducts from the end of DNA strand breaks. Tdp1 specifically catalyzes the hydrolysis of phosphodiester linked DNA-adducts. These DNA lesions range from damaged nucleotides to peptide-DNA adducts to protein-DNA covalent complexes and are products of endogenously or exogenously induced insults or simply failed reaction products. These adducts include DNA inserted ribonucleotides and non-conventional nucleotides, as well as covalent reaction intermediates of DNA topoisomerases with DNA and a Tdp1-DNA adduct in trans. This implies that Tdp1 plays a role in maintaining genome stability and cellular homeostasis. Dysregulation of Tdp1 protein levels or catalysis shifts the equilibrium to genome instability and is associated with driving human pathologies such as cancer and neurodegeneration. In this review, we highlight the function of the N-terminal domain of Tdp1. This domain is understudied, structurally unresolved, and the least conserved in amino acid sequence and length compared to the rest of the enzyme. However, over time it emerged that the N-terminal domain was post-translationally modified by, among others, phosphorylation, SUMOylation, and Ubiquitinoylation, which regulate Tdp1 protein interactions with other DNA repair associated proteins, cellular localization, and Tdp1 protein stability.
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