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https://www.readbyqxmd.com/read/28203566/increased-spontaneous-recombination-in-rnase-h2-deficient-cells-arises-from-multiple-contiguous-rnmps-and-not-from-single-rnmp-residues-incorporated-by-dna-polymerase-epsilon
#1
Anastasiya Epshtein, Catherine J Potenski, Hannah L Klein
Ribonucleotides can become embedded in DNA from insertion by DNA polymerases, failure to remove Okazaki fragment primers, R-loops that can prime replication, and RNA/cDNA-mediated recombination. RNA:DNA hybrids are removed by RNase H enzymes. Single rNMPs in DNA are removed by RNase H2 and if they remain on the leading strand, can lead to mutagenesis in a Top1-dependent pathway. rNMPs in DNA can also stimulate genome instability, among which are homologous recombination gene conversion events. We previously found that, similar to the rNMP-stimulated mutagenesis, rNMP-stimulated recombination was also Top1-dependent...
June 2016: Microbial Cell
https://www.readbyqxmd.com/read/28098815/replication-fork-protection-factors-controlling-r-loop-bypass-and-suppression
#2
REVIEW
Emily Yun-Chia Chang, Peter C Stirling
Replication-transcription conflicts have been a well-studied source of genome instability for many years and have frequently been linked to defects in RNA processing. However, recent characterization of replication fork-associated proteins has revealed that defects in fork protection can directly or indirectly stabilize R-loop structures in the genome and promote transcription-replication conflicts that lead to genome instability. Defects in essential DNA replication-associated activities like topoisomerase, or the minichromosome maintenance (MCM) helicase complex, as well as fork-associated protection factors like the Fanconi anemia pathway, both appear to mitigate transcription-replication conflicts...
January 14, 2017: Genes
https://www.readbyqxmd.com/read/28076779/transcription-dynamics-prevent-rna-mediated-genomic-instability-through-srpk2-dependent-ddx23-phosphorylation
#3
Sreerama Chaitanya Sridhara, Sílvia Carvalho, Ana Rita Grosso, Lina Marcela Gallego-Paez, Maria Carmo-Fonseca, Sérgio Fernandes de Almeida
Genomic instability is frequently caused by nucleic acid structures termed R-loops that are formed during transcription. Despite their harmful potential, mechanisms that sense, signal, and suppress these structures remain elusive. Here, we report that oscillations in transcription dynamics are a major sensor of R-loops. We show that pausing of RNA polymerase II (RNA Pol II) initiates a signaling cascade whereby the serine/arginine protein kinase 2 (SRPK2) phosphorylates the DDX23 helicase, culminating in the suppression of R-loops...
January 10, 2017: Cell Reports
https://www.readbyqxmd.com/read/28065739/r-loop-depletion-by-over-expressed-rnase-h1-in-mouse-b-cells-increases-activation-induced-deaminase-access-to-the-transcribed-strand-without-altering-frequency-of-isotype-switching
#4
Robert W Maul, Hyongi Chon, Kiran Sakhuja, Susana M Cerritelli, Lina A Gugliotti, Patricia J Gearhart, Robert J Crouch
R-loops, three-strand structures consisting of mRNA hybridized to the complementary DNA and a single-stranded DNA loop, are formed in switch regions on the heavy-chain immunoglobulin locus. To determine if R-loops have a direct effect on any of the steps involved in isotype switching, we generated a transgenic mouse that over-expressed RNase H1, an enzyme that cleaves the RNA of RNA/DNA hybrids in B cells. R-loops in the switch μ region were depleted by 70% in ex vivo activated splenic B cells. Frequencies of isotype switching to IgG1, IgG2b, IgG2c, and IgG3 were the same as C57BL/6 control cells...
January 6, 2017: Journal of Molecular Biology
https://www.readbyqxmd.com/read/28062037/single-molecule-insight-into-target-recognition-by-crispr-cas-complexes
#5
M Rutkauskas, A Krivoy, M D Szczelkun, C Rouillon, R Seidel
Ribonucleoprotein (RNP) complexes from CRISPR-Cas systems have attracted enormous interest since they can be easily and flexibly reprogrammed to target any desired locus for genome engineering and gene regulation applications. Basis for the programmability is a short RNA (crRNA) inside these complexes that recognizes the target nucleic acid by base pairing. For CRISPR-Cas systems that target double-stranded DNA this results in local DNA unwinding and formation of a so-called R-loop structure. Here we provide an overview how this target recognition mechanism can be dissected in great detail at the level of a single molecule...
2017: Methods in Enzymology
https://www.readbyqxmd.com/read/27991914/the-spliceosome-u2-snrnp-factors-promote-genome-stability-through-distinct-mechanisms-transcription-of-repair-factors-and-r-loop-processing
#6
M Tanikawa, K Sanjiv, T Helleday, P Herr, O Mortusewicz
Recent whole-exome sequencing of malignancies have detected recurrent somatic mutations in U2 small nuclear ribonucleoprotein complex (snRNP) components of the spliceosome. These factors have also been identified as novel players in the DNA-damage response (DDR) in several genome-wide screens and proteomic analysis. Although accumulating evidence implies that the spliceosome has an important role in genome stability and is an emerging hallmark of cancer, its precise role in DNA repair still remains elusive...
December 19, 2016: Oncogenesis
https://www.readbyqxmd.com/read/27991904/pif1-family-helicases-cooperatively-suppress-widespread-replication-fork-arrest-at-trna-genes
#7
Joseph S Osmundson, Jayashree Kumar, Rani Yeung, Duncan J Smith
Saccharomyces cerevisiae expresses two Pif1-family helicases-Pif1 and Rrm3-which have been reported to play distinct roles in numerous nuclear processes. Here, we systematically characterized the roles of Pif1 helicases in replisome progression and lagging-strand synthesis in S. cerevisiae. We demonstrate that either Pif1 or Rrm3 redundantly stimulates strand displacement by DNA polymerase δ during lagging-strand synthesis. By analyzing replisome mobility in pif1 and rrm3 mutants, we show that Rrm3, with a partially redundant contribution from Pif1, suppresses widespread terminal arrest of the replisome at tRNA genes...
February 2017: Nature Structural & Molecular Biology
https://www.readbyqxmd.com/read/27974207/dna-replication-origins-in-immunoglobulin-switch-regions-regulate-class-switch-recombination-in-an-r-loop-dependent-manner
#8
Eva-Maria Wiedemann, Mihaela Peycheva, Rushad Pavri
Class switch recombination (CSR) at the immunoglobulin heavy chain (IgH) locus generates antibody isotypes. CSR depends on double-strand breaks (DSBs) induced by activation-induced cytidine deaminase (AID). Although DSB formation and repair machineries are active in G1 phase, efficient CSR is dependent on cell proliferation and S phase entry; however, the underlying mechanisms are obscure. Here, we show that efficient CSR requires the replicative helicase, the Mcm complex. Mcm proteins are enriched at IgH switch regions during CSR, leading to assembly of facultative replication origins that require Mcm helicase function for productive CSR...
December 13, 2016: Cell Reports
https://www.readbyqxmd.com/read/27938663/rnase-h-enables-efficient-repair-of-r-loop-induced-dna-damage
#9
Jeremy D Amon, Douglas Koshland
R-loops, three-stranded structures that form when transcripts hybridize to chromosomal DNA, are potent agents of genome instability. This instability has been explained by the ability of R-loops to induce DNA damage. Here, we show that persistent R-loops also compromise DNA repair. Depleting endogenous RNase H activity impairs R-loop removal in Saccharomyces cerevisiae, causing DNA damage that occurs preferentially in the repetitive ribosomal DNA locus (rDNA). We analyzed the repair kinetics of this damage and identified mutants that modulate repair...
December 10, 2016: ELife
https://www.readbyqxmd.com/read/27899586/r-loopdb-a-database-for-r-loop-forming-sequences-rlfs-and-r-loops
#10
Piroon Jenjaroenpun, Thidathip Wongsurawat, Sawannee Sutheeworapong, Vladimir A Kuznetsov
R-loopDB (http://rloop.bii.a-star.edu.sg) was originally constructed as a collection of computationally predicted R-loop forming sequences (RLFSs) in the human genic regions. The renewed R-loopDB provides updates, improvements and new options, including access to recent experimental data. It includes genome-scale prediction of RLFSs for humans, six other animals and yeast. Using the extended quantitative model of RLFSs (QmRLFS), we significantly increased the number of RLFSs predicted in the human genes and identified RLFSs in other organism genomes...
January 4, 2017: Nucleic Acids Research
https://www.readbyqxmd.com/read/27863397/targeting-gli-by-gant61-involves-mechanisms-dependent-on-inhibition-of-both-transcription-and-dna-licensing
#11
Ruowen Zhang, Jiahui Wu, Sylvain Ferrandon, Katie J Glowacki, Janet A Houghton
The GLI genes are transcription factors and in cancers are oncogenes, aberrantly and constitutively activated. GANT61, a specific GLI inhibitor, has induced extensive cytotoxicity in human models of colon cancer. The FOXM1 promoter was determined to be a transcriptional target of GLI1. In HT29 cells, inhibition of GLI1 binding at the GLI consensus sequence by GANT61 led to inhibited binding of Pol II, the pause-release factors DSIF, NELF and p-TEFb. The formation of R-loops (RNA:DNA hybrids, ssDNA), were reduced by GANT61 at the FOXM1 promoter...
November 15, 2016: Oncotarget
https://www.readbyqxmd.com/read/27851891/traveling-rocky-roads-the-consequences-of-transcription-blocking-dna-lesions-on-rna-polymerase-ii
#12
REVIEW
Barbara Steurer, Jurgen A Marteijn
The faithful transcription of eukaryotic genes by RNA polymerase II (RNAP2) is crucial for proper cell function and tissue homeostasis. However, transcription-blocking DNA lesions of both an endogenous and environmental origin continuously challenge the progression of elongating RNAP2. The stalling of RNAP2 on a transcription-blocking lesion triggers a series of highly regulated events, including RNAP2 processing to make the lesion accessible for DNA repair, R-loop-mediated DNA damage signaling, and the initiation of transcription-coupled DNA repair...
November 13, 2016: Journal of Molecular Biology
https://www.readbyqxmd.com/read/27849576/two-familial-als-proteins-function-in-prevention-repair-of-transcription-associated-dna-damage
#13
Sarah J Hill, Daniel A Mordes, Lisa A Cameron, Donna S Neuberg, Serena Landini, Kevin Eggan, David M Livingston
Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron dysfunction disease that leads to paralysis and death. There is currently no established molecular pathogenesis pathway. Multiple proteins involved in RNA processing are linked to ALS, including FUS and TDP43, and we propose a disease mechanism in which loss of function of at least one of these proteins leads to an accumulation of transcription-associated DNA damage contributing to motor neuron cell death and progressive neurological symptoms...
November 29, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27846236/disruption-of-higher-order-dna-structures-in-friedreich-s-ataxia-gaa-n-repeats-by-pna-or-lna-targeting
#14
Helen Bergquist, Cristina S J Rocha, Rubén Álvarez-Asencio, Chi-Hung Nguyen, Mark W Rutland, C I Edvard Smith, Liam Good, Peter E Nielsen, Rula Zain
Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich's ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)n expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)n repeats of different lengths (short: n=9, medium: n=75 or long: n=115) by chemical probing of triple helical and single stranded regions...
2016: PloS One
https://www.readbyqxmd.com/read/27804953/structural-roles-of-guide-rnas-in-the-nuclease-activity-of-cas9-endonuclease
#15
Youngbin Lim, So Young Bak, Keewon Sung, Euihwan Jeong, Seung Hwan Lee, Jin-Soo Kim, Sangsu Bae, Seong Keun Kim
The type II CRISPR-associated protein Cas9 recognizes and cleaves target DNA with the help of two guide RNAs (gRNAs; tracrRNA and crRNA). However, the detailed mechanisms and kinetics of these gRNAs in the Cas9 nuclease activity are unclear. Here, we investigate the structural roles of gRNAs in the CRISPR-Cas9 system by single-molecule spectroscopy and reveal a new conformation of inactive Cas9 that is thermodynamically more preferable than active apo-Cas9. We find that tracrRNA prevents Cas9 from changing into the inactive form and leads to the Cas9:gRNA complex...
November 2, 2016: Nature Communications
https://www.readbyqxmd.com/read/27796495/transcription-replication-conflicts-at-chromosomal-fragile-sites-consequences-in-m-phase-and-beyond
#16
REVIEW
Vibe H Oestergaard, Michael Lisby
Collision between the molecular machineries responsible for transcription and replication is an important source of genome instability. Certain transcribed regions known as chromosomal fragile sites are particularly prone to recombine and mutate in a manner that correlates with specific transcription and replication patterns. At the same time, these chromosomal fragile sites engage in aberrant DNA structures in mitosis. Here, we discuss the mechanistic details of transcription-replication conflicts including putative scenarios for R-loop-induced replication inhibition to understand how transcription-replication conflicts transition from S phase into various aberrant DNA structures in mitosis...
October 28, 2016: Chromosoma
https://www.readbyqxmd.com/read/27793359/nascent-connections-r-loops-and-chromatin-patterning
#17
REVIEW
Frédéric Chédin
RNA molecules, such as long noncoding RNAs (lncRNAs), have critical roles in regulating gene expression, chromosome architecture, and the modification states of chromatin. Recent developments suggest that RNA also influences gene expression and chromatin patterns through the interaction of nascent transcripts with their DNA template via the formation of co-transcriptional R-loop structures. R-loop formation over specific, conserved, hotspots occurs at thousands of genes in mammalian genomes and represents an important and dynamic feature of mammalian chromatin...
December 2016: Trends in Genetics: TIG
https://www.readbyqxmd.com/read/27787508/dangerous-r-loops-form-in-the-absence-of-h3k9-methylation
#18
Anna Elisabetta Salcini
Methylation of histone H3 on lysine 9 (H3K9) is a hallmark of transcriptionally inactive heterochromatin that is deregulated in pathological conditions. A new study shows that complete loss of H3K9 methylation in Caenorhabditis elegans leads to derepression of repetitive elements and formation of DNA:RNA hybrids (R loops), resulting in increased rates of repeat-specific mutation.
October 27, 2016: Nature Genetics
https://www.readbyqxmd.com/read/27771483/senataxin-genome-guardian-at-the-interface-of-transcription-and-neurodegeneration
#19
Matthias Groh, Laura Oana Albulescu, Agnese Cristini, Natalia Gromak
R-loops comprise an RNA/DNA hybrid and displaced single-stranded DNA. They play crucial biological functions and are implicated in neurological diseases, including ataxias, amyotrophic lateral sclerosis, nucleotide expansion disorders (Friedreich ataxia, Fragile X syndrome) and cancer. Currently it is unclear which mechanisms cause R-loops structures to become pathogenic. The RNA/DNA helicase Senataxin (SETX) is one of the best characterised R-loop-binding factors in vivo. Mutations in SETX are linked to two neurodegenerative disorders: ataxia with oculomotor apraxia type 2 (AOA2) and amyotrophic lateral sclerosis type 4 (ALS4)...
October 19, 2016: Journal of Molecular Biology
https://www.readbyqxmd.com/read/27725641/increased-global-transcription-activity-as-a-mechanism-of-replication-stress-in-cancer
#20
Panagiotis Kotsantis, Lara Marques Silva, Sarah Irmscher, Rebecca M Jones, Lisa Folkes, Natalia Gromak, Eva Petermann
Cancer is a disease associated with genomic instability that often results from oncogene activation. This in turn leads to hyperproliferation and replication stress. However, the molecular mechanisms that underlie oncogene-induced replication stress are still poorly understood. Oncogenes such as HRAS(V12) promote proliferation by upregulating general transcription factors to stimulate RNA synthesis. Here we investigate whether this increase in transcription underlies oncogene-induced replication stress. We show that in cells overexpressing HRAS(V12), elevated expression of the general transcription factor TATA-box binding protein (TBP) leads to increased RNA synthesis, which together with R-loop accumulation results in replication fork slowing and DNA damage...
October 11, 2016: Nature Communications
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