scholarly journals High Flexibility of RNaseH2 Catalytic Activity with Respect to Non-Canonical DNA Structures

2021 ◽  
Vol 22 (10) ◽  
pp. 5201
Author(s):  
Maria Dede ◽  
Silvia Napolitano ◽  
Anna Melati ◽  
Valentina Pirota ◽  
Giovanni Maga ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Genome Instability ◽  
Excision Repair ◽  
Dna Lesions ◽  
Hydroxyl Group ◽  
Dna Structures ◽  
Geometrical Features ◽  
Fork Stalling ◽  
High Flexibility ◽  
Rnase H2

Ribonucleotides misincorporated in the human genome are the most abundant DNA lesions. The 2′-hydroxyl group makes them prone to spontaneous hydrolysis, potentially resulting in strand breaks. Moreover, their presence may decrease the rate of DNA replication causing replicative fork stalling and collapse. Ribonucleotide removal is initiated by Ribonuclease H2 (RNase H2), the key player in Ribonucleotide Excision Repair (RER). Its absence leads to embryonic lethality in mice, while mutations decreasing its activity cause Aicardi–Goutières syndrome. DNA geometry can be altered by DNA lesions or by peculiar sequences forming secondary structures, like G-quadruplex (G4) and trinucleotide repeats (TNR) hairpins, which significantly differ from canonical B-form. Ribonucleotides pairing to lesioned nucleotides, or incorporated within non-B DNA structures could avoid RNase H2 recognition, potentially contributing to genome instability. In this work, we investigate the ability of RNase H2 to process misincorporated ribonucleotides in a panel of DNA substrates showing different geometrical features. RNase H2 proved to be a flexible enzyme, recognizing as a substrate the majority of the constructs we generated. However, some geometrical features and non-canonical DNA structures severely impaired its activity, suggesting a relevant role of misincorporated ribonucleotides in the physiological instability of specific DNA sequences.

scholarly journals Role of Base Excision Repair Pathway in the Processing of Complex DNA Damage Generated by Oxidative Stress and Anticancer Drugs

2021 ◽  
Vol 8 ◽  
Author(s):  
Yeldar Baiken ◽  
Damira Kanayeva ◽  
Sabira Taipakova ◽  
Regina Groisman ◽  
Alexander A. Ishchenko ◽  
...  
Keyword(s):  
Dna Damage ◽  
Base Excision Repair ◽  
Genome Instability ◽  
Excision Repair ◽  
Chromosomal Rearrangements ◽  
Strand Break ◽  
Dna Lesions ◽  
Complex Nature ◽  
Base Excision

Chemical alterations in DNA induced by genotoxic factors can have a complex nature such as bulky DNA adducts, interstrand DNA cross-links (ICLs), and clustered DNA lesions (including double-strand breaks, DSB). Complex DNA damage (CDD) has a complex character/structure as compared to singular lesions like randomly distributed abasic sites, deaminated, alkylated, and oxidized DNA bases. CDD is thought to be critical since they are more challenging to repair than singular lesions. Although CDD naturally constitutes a relatively minor fraction of the overall DNA damage induced by free radicals, DNA cross-linking agents, and ionizing radiation, if left unrepaired, these lesions cause a number of serious consequences, such as gross chromosomal rearrangements and genome instability. If not tightly controlled, the repair of ICLs and clustered bi-stranded oxidized bases via DNA excision repair will either inhibit initial steps of repair or produce persistent chromosomal breaks and consequently be lethal for the cells. Biochemical and genetic evidences indicate that the removal of CDD requires concurrent involvement of a number of distinct DNA repair pathways including poly(ADP-ribose) polymerase (PARP)-mediated DNA strand break repair, base excision repair (BER), nucleotide incision repair (NIR), global genome and transcription coupled nucleotide excision repair (GG-NER and TC-NER, respectively), mismatch repair (MMR), homologous recombination (HR), non-homologous end joining (NHEJ), and translesion DNA synthesis (TLS) pathways. In this review, we describe the role of DNA glycosylase-mediated BER pathway in the removal of complex DNA lesions.

scholarly journals Impact of DNA sequences in the DNA duplex opening by the Rad4/XPC nucleotide excision repair complex

2020 ◽  
Author(s):  
Debamita Paul ◽  
Hong Mu ◽  
Qing Dai ◽  
Amirrasoul Tavakoli ◽  
Chuan He ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Nucleotide Excision Repair ◽  
Dna Sequences ◽  
Excision Repair ◽  
Md Simulations ◽  
Dna Duplex ◽  
Open Structure ◽  
Dna Structures ◽  
Reverse Mode ◽  
Nucleotide Excision

ABSTRACTRad4/XPC is a key DNA damage sensor for nucleotide excision repair (NER) in eukaryotes. Rad4/XPC recognizes diverse bulky lesions by flipping out two lesion-containing nucleotide pairs and inserting a β-hairpin from the BHD3 domain (β-hairpin3) into the DNA duplex. We have previously observed that Rad4 can form the same ‘open’ structure when covalently tethered to a normal DNA sequence containing consecutive C/G’s (CCC/GGG) and that a similar open-like structure can be formed even when the β-hairpin3 is lacking. Here, we report a crystal structure of the Δβ-hairpin3 mutant tethered to a sequence containing alternating C/G’s (CGC/GCG). In contrast to the previous structures, Rad4 bound to CGC/GCG in a 180°-reversed manner, capping the end of the duplex without flipping out the nucleotides. MD simulations showed that CGC/GCG was inherently less ‘openable’ than CCC/GGG and that Rad4 failed to engage with its minor groove, a hallmark of productive binding towards ‘opening’. These results reveal that DNA sequences significantly influence the thermodynamic barrier for DNA opening by Rad4, which may render certain DNA structures/sequences resistant to ‘opening’ despite a long residence time of Rad4. The reverse- mode may indicate unproductive binding for NER whereas the DNA end-binding may hint at Rad4/XPC’s functions beyond NER.

scholarly journals DDB1 Maintains Genome Integrity through Regulation of Cdt1

2006 ◽  
Vol 26 (21) ◽  
pp. 7977-7990 ◽  
Author(s):  
Courtney A. Lovejoy ◽  
Kimberli Lock ◽  
Ashwini Yenamandra ◽  
David Cortez
Keyword(s):  
Dna Damage ◽  
Genome Stability ◽  
Genome Instability ◽  
Excision Repair ◽  
Dna Lesions ◽  
Cell Cycle Checkpoints ◽  
Dna Double Strand Breaks ◽  
Genome Maintenance ◽  
Strand Breaks ◽  
Ubiquitin Ligase Complex

ABSTRACT DDB1, a component of a Cul4A ubiquitin ligase complex, promotes nucleotide excision repair (NER) and regulates DNA replication. We have investigated the role of human DDB1 in maintaining genome stability. DDB1-depleted cells accumulate DNA double-strand breaks in widely dispersed regions throughout the genome and have activated ATM and ATR cell cycle checkpoints. Depletion of Cul4A yields similar phenotypes, indicating that an E3 ligase function of DDB1 is important for genome maintenance. In contrast, depletion of DDB2, XPA, or XPC does not cause activation of DNA damage checkpoints, indicating that defects in NER are not involved. One substrate of DDB1-Cul4A that is crucial for preventing genome instability is Cdt1. DDB1-depleted cells exhibit increased levels of Cdt1 protein and rereplication, despite containing other Cdt1 regulatory mechanisms. The rereplication, accumulation of DNA damage, and activation of checkpoint responses in DDB1-depleted cells require entry into S phase and are partially, but not completely, suppressed by codepletion of Cdt1. Therefore, DDB1 prevents DNA lesions from accumulating in replicating human cells, in part by regulating Cdt1 degradation.

scholarly journals Bypassing a 8,5′-cyclo-2′-deoxyadenosine lesion by human DNA polymerase η at atomic resolution

2018 ◽  
Vol 115 (42) ◽  
pp. 10660-10665 ◽  
Author(s):  
Peter J. Weng ◽  
Yang Gao ◽  
Mark T. Gregory ◽  
Pengcheng Wang ◽  
Yinsheng Wang ◽  
...  
Keyword(s):  
Excision Repair ◽  
Dna Lesions ◽  
Dna Structures ◽  
Extra Space ◽  
Human Dna ◽  
Nucleotide Excision ◽  
Mutagenic Property ◽  
Structural Insights ◽  
Protein Environment ◽  
Adenine Base

Oxidatively induced DNA lesions 8,5′-cyclopurine-2′-deoxynucleosides (cdPus) are prevalent and cytotoxic by impeding DNA replication and transcription. Both the 5′R- and 5′S-diastereomers of cdPu can be removed by nucleotide excision repair; however, the 5′S-cdPu is more resistant to repair than the 5′R counterpart. Here, we report the crystal structures of human polymerase (Pol) η bypassing 5′S-8,5′-cyclo-2′-deoxyadenosine (cdA) in insertion and the following two extension steps. The cdA-containing DNA structures vary in response to the protein environment. Supported by the “molecular splint” of Pol η, the structure of 5′S-cdA at 1.75-Å resolution reveals that the backbone is pinched toward the minor groove and the adenine base is tilted. In the templating position, the cdA takes up the extra space usually reserved for the thymine dimer, and dTTP is efficiently incorporated by Pol η in the presence of Mn2+. Rigid distortions of the DNA duplex by cdA, however, prevent normal base pairing and hinder immediate primer extension by Pol η. Our results provide structural insights into the strong replication blockage effect and the mutagenic property of the cdPu lesions in cells.

scholarly journals High density of unrepaired genomic ribonucleotides leads to Topoisomerase 1-mediated severe growth defects in absence of ribonucleotide reductase

2020 ◽  
Vol 48 (8) ◽  
pp. 4274-4297 ◽  
Author(s):  
Susana M Cerritelli ◽  
Jaime Iranzo ◽  
Sushma Sharma ◽  
Andrei Chabes ◽  
Robert J Crouch ◽  
...  
Keyword(s):  
Ribonucleotide Reductase ◽  
Genomic Dna ◽  
Genome Instability ◽  
Excision Repair ◽  
Topoisomerase 1 ◽  
Growth Defects ◽  
Rnase H2 ◽  
Cell Lethality ◽  
Severe Growth ◽  
Excessive Accumulation

Abstract Cellular levels of ribonucleoside triphosphates (rNTPs) are much higher than those of deoxyribonucleoside triphosphates (dNTPs), thereby influencing the frequency of incorporation of ribonucleoside monophosphates (rNMPs) by DNA polymerases (Pol) into DNA. RNase H2-initiated ribonucleotide excision repair (RER) efficiently removes single rNMPs in genomic DNA. However, processing of rNMPs by Topoisomerase 1 (Top1) in absence of RER induces mutations and genome instability. Here, we greatly increased the abundance of genomic rNMPs in Saccharomyces cerevisiae by depleting Rnr1, the major subunit of ribonucleotide reductase, which converts ribonucleotides to deoxyribonucleotides. We found that in strains that are depleted of Rnr1, RER-deficient, and harbor an rNTP-permissive replicative Pol mutant, excessive accumulation of single genomic rNMPs severely compromised growth, but this was reversed in absence of Top1. Thus, under Rnr1 depletion, limited dNTP pools slow DNA synthesis by replicative Pols and provoke the incorporation of high levels of rNMPs in genomic DNA. If a threshold of single genomic rNMPs is exceeded in absence of RER and presence of limited dNTP pools, Top1-mediated genome instability leads to severe growth defects. Finally, we provide evidence showing that accumulation of RNA/DNA hybrids in absence of RNase H1 and RNase H2 leads to cell lethality under Rnr1 depletion.

scholarly journals Structural insights into the recognition of cisplatin and AAF-dG lesion by Rad14 (XPA)

2015 ◽  
Vol 112 (27) ◽  
pp. 8272-8277 ◽  
Author(s):  
Sandra C. Koch ◽  
Jochen Kuper ◽  
Karola L. Gasteiger ◽  
Nina Simon ◽  
Ralf Strasser ◽  
...  
Keyword(s):  
Excision Repair ◽  
Dna Lesions ◽  
General Mechanism ◽  
Dna Duplexes ◽  
Central Importance ◽  
Dna Structures ◽  
Cancer Predisposition Syndrome ◽  
Recognition Motif ◽  
Nucleotide Excision ◽  
Structural Insights

Nucleotide excision repair (NER) is responsible for the removal of a large variety of structurally diverse DNA lesions. Mutations of the involved proteins cause the xeroderma pigmentosum (XP) cancer predisposition syndrome. Although the general mechanism of the NER process is well studied, the function of the XPA protein, which is of central importance for successful NER, has remained enigmatic. It is known, that XPA binds kinked DNA structures and that it interacts also with DNA duplexes containing certain lesions, but the mechanism of interactions is unknown. Here we present two crystal structures of the DNA binding domain (DBD) of the yeast XPA homolog Rad14 bound to DNA with either a cisplatin lesion (1,2-GG) or an acetylaminofluorene adduct (AAF-dG). In the structures, we see that two Rad14 molecules bind to the duplex, which induces DNA melting of the duplex remote from the lesion. Each monomer interrogates the duplex with a β-hairpin, which creates a 13mer duplex recognition motif additionally characterized by a sharp 70° DNA kink at the position of the lesion. Although the 1,2-GG lesion stabilizes the kink due to the covalent fixation of the crosslinked dG bases at a 90° angle, the AAF-dG fully intercalates into the duplex to stabilize the kinked structure.

scholarly journals Excision of Oxidatively Generated Guanine Lesions by Competitive DNA Repair Pathways

2021 ◽  
Vol 22 (5) ◽  
pp. 2698
Author(s):  
Vladimir Shafirovich ◽  
Nicholas E. Geacintov
Keyword(s):  
Excision Repair ◽  
Dna Lesions ◽  
Dna Templates ◽  
Circular Dna ◽  
Damage Sensing ◽  
Cell Extracts ◽  
Dna Base ◽  
Nucleotide Excision ◽  
Repair Pathways ◽  
Cellular Dna

The base and nucleotide excision repair pathways (BER and NER, respectively) are two major mechanisms that remove DNA lesions formed by the reactions of genotoxic intermediates with cellular DNA. It is generally believed that small non-bulky oxidatively generated DNA base modifications are removed by BER pathways, whereas DNA helix-distorting bulky lesions derived from the attack of chemical carcinogens or UV irradiation are repaired by the NER machinery. However, existing and growing experimental evidence indicates that oxidatively generated DNA lesions can be repaired by competitive BER and NER pathways in human cell extracts and intact human cells. Here, we focus on the interplay and competition of BER and NER pathways in excising oxidatively generated guanine lesions site-specifically positioned in plasmid DNA templates constructed by a gapped-vector technology. These experiments demonstrate a significant enhancement of the NER yields in covalently closed circular DNA plasmids (relative to the same, but linearized form of the same plasmid) harboring certain oxidatively generated guanine lesions. The interplay between the BER and NER pathways that remove oxidatively generated guanine lesions are reviewed and discussed in terms of competitive binding of the BER proteins and the DNA damage-sensing NER factor XPC-RAD23B to these lesions.

scholarly journals The splicing factor XAB2 interacts with ERCC1-XPF and XPG for R-loop processing

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Evi Goulielmaki ◽  
Maria Tsekrekou ◽  
Nikos Batsiotos ◽  
Mariana Ascensão-Ferreira ◽  
Eleftheria Ledaki ◽  
...  
Keyword(s):  
Dna Damage ◽  
Rna Splicing ◽  
Excision Repair ◽  
Intron Retention ◽  
Dna Lesions ◽  
Splicing Factor ◽  
Loop Formation ◽  
Rna Targets ◽  
Underlying Mechanisms

AbstractRNA splicing, transcription and the DNA damage response are intriguingly linked in mammals but the underlying mechanisms remain poorly understood. Using an in vivo biotinylation tagging approach in mice, we show that the splicing factor XAB2 interacts with the core spliceosome and that it binds to spliceosomal U4 and U6 snRNAs and pre-mRNAs in developing livers. XAB2 depletion leads to aberrant intron retention, R-loop formation and DNA damage in cells. Studies in illudin S-treated cells and Csbm/m developing livers reveal that transcription-blocking DNA lesions trigger the release of XAB2 from all RNA targets tested. Immunoprecipitation studies reveal that XAB2 interacts with ERCC1-XPF and XPG endonucleases outside nucleotide excision repair and that the trimeric protein complex binds RNA:DNA hybrids under conditions that favor the formation of R-loops. Thus, XAB2 functionally links the spliceosomal response to DNA damage with R-loop processing with important ramifications for transcription-coupled DNA repair disorders.

scholarly journals Telomeric DNA sequences in beetle taxa vary with species richness

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Daniela Prušáková ◽  
Vratislav Peska ◽  
Stano Pekár ◽  
Michal Bubeník ◽  
Lukáš Čížek ◽  
...  
Keyword(s):  
Species Richness ◽  
Dna Sequences ◽  
Genome Instability ◽  
Telomeric Sequence ◽  
Dna Repeats ◽  
Telomeric Dna ◽  
Common Pattern ◽  
Telomeric Sequences ◽  
Genomic Changes ◽  
Protective Structures

AbstractTelomeres are protective structures at the ends of eukaryotic chromosomes, and disruption of their nucleoprotein composition usually results in genome instability and cell death. Telomeric DNA sequences have generally been found to be exceptionally conserved in evolution, and the most common pattern of telomeric sequences across eukaryotes is (TxAyGz)n maintained by telomerase. However, telomerase-added DNA repeats in some insect taxa frequently vary, show unusual features, and can even be absent. It has been speculated about factors that might allow frequent changes in telomere composition in Insecta. Coleoptera (beetles) is the largest of all insect orders and based on previously available data, it seemed that the telomeric sequence of beetles varies to a great extent. We performed an extensive mapping of the (TTAGG)n sequence, the ancestral telomeric sequence in Insects, across the main branches of Coleoptera. Our study indicates that the (TTAGG)n sequence has been repeatedly or completely lost in more than half of the tested beetle superfamilies. Although the exact telomeric motif in most of the (TTAGG)n-negative beetles is unknown, we found that the (TTAGG)n sequence has been replaced by two alternative telomeric motifs, the (TCAGG)n and (TTAGGG)n, in at least three superfamilies of Coleoptera. The diversity of the telomeric motifs was positively related to the species richness of taxa, regardless of the age of the taxa. The presence/absence of the (TTAGG)n sequence highly varied within the Curculionoidea, Chrysomeloidea, and Staphylinoidea, which are the three most diverse superfamilies within Metazoa. Our data supports the hypothesis that telomere dysfunctions can initiate rapid genomic changes that lead to reproductive isolation and speciation.

scholarly journals Non-B DNA-Forming Motifs Promote Mfd-Dependent Stationary-Phase Mutagenesis in Bacillus subtilis

2021 ◽  
Vol 9 (6) ◽  
pp. 1284
Author(s):  
Tatiana Ermi ◽  
Carmen Vallin ◽  
Ana Gabriela Regalado García ◽  
Moises Bravo ◽  
Ismaray Fernandez Cordero ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Stationary Phase ◽  
Genome Instability ◽  
Mutagenic Effect ◽  
Genetic Changes ◽  
Dna Structures ◽  
Coding Regions ◽  
G4 Dna ◽  
Stressed Cells ◽  
Growing Conditions

Transcription-induced mutagenic mechanisms limit genetic changes to times when expression happens and to coding DNA. It has been hypothesized that intrinsic sequences that have the potential to form alternate DNA structures, such as non-B DNA structures, influence these mechanisms. Non-B DNA structures are promoted by transcription and induce genome instability in eukaryotic cells, but their impact in bacterial genomes is less known. Here, we investigated if G4 DNA- and hairpin-forming motifs influence stationary-phase mutagenesis in Bacillus subtilis. We developed a system to measure the influence of non-B DNA on B. subtilis stationary-phase mutagenesis by deleting the wild-type argF at its chromosomal position and introducing IPTG-inducible argF alleles differing in their ability to form hairpin and G4 DNA structures into an ectopic locus. Using this system, we found that sequences predicted to form non-B DNA structures promoted mutagenesis in B. subtilis stationary-phase cells; such a response did not occur in growing conditions. We also found that the transcription-coupled repair factor Mfd promoted mutagenesis at these predicted structures. In summary, we showed that non-B DNA-forming motifs promote genetic instability, particularly in coding regions in stressed cells; therefore, non-B DNA structures may have a spatial and temporal mutagenic effect in bacteria. This study provides insights into mechanisms that prevent or promote mutagenesis and advances our understanding of processes underlying bacterial evolution.

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