| 1. |
- Gupta, Amitabha, et al.
(författare)
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Telomere Length Homeostasis Responds to Changes in Intracellular dNTP Pools
- 2013
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Ingår i: Genetics. - : The Genetics Society. - 0016-6731 .- 1943-2631. ; 193:4, s. 1095-1105
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Tidskriftsartikel (refereegranskat)abstract
- Telomeres, the ends of linear eukaryotic chromosomes, shorten due to incomplete DNA replication and nucleolytic degradation. Cells counteract this shortening by employing a specialized reverse transcriptase called telomerase, which uses deoxyribonucleoside triphosphates (dNTPs) to extend telomeres. Intracellular dNTP levels are tightly regulated and perturbation of these levels is known to affect DNA synthesis. We examined whether altering the levels of the dNTP pools or changing the relative ratios of the four dNTPs in Saccharomyces cerevisiae would affect the length of the telomeres. Lowering dNTP levels leads to a modest shortening of telomeres, while increasing dNTP pools has no significant effect on telomere length. Strikingly, altering the ratio of the four dNTPs dramatically affects telomere length homeostasis, both positively and negatively. Specifically, we find that intracellular dGTP levels positively correlate with both telomere length and telomerase nucleotide addition processivity in vivo. Our findings are consistent with in vitro data showing dGTP-dependent stimulation of telomerase activity in multiple organisms, and suggest that telomerase activity is modulated in vivo by dGTP levels.
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| 2. |
- Ragu, Sandrine, et al.
(författare)
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Loss of the thioredoxin reductase Trr1 suppresses the genomic instability of peroxiredoxin tsa1 mutants
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- The absence of Tsa1, a key peroxiredoxin that scavenges H2O2 in Saccharomyces cerevisiae, causes the accumulation of a broad spectrum of mutations. Deletion of TSA1 also causes synthetic lethality in combination with mutations in RAD51 or several key genes involved in DNA double-strand break repair. In the present study, we propose that the accumulation of reactive oxygen species (ROS) is the primary cause of genome instability of tsa1 Delta cells. In searching for spontaneous suppressors of synthetic lethality of tsa1 Delta rad51 Delta double mutants, we identified that the loss of thioredoxin reductase Trr1 rescues their viability. The trr1 Delta mutant displayed a Can(R) mutation rate 5-fold lower than wild-type cells. Additional deletion of TRR1 in tsa1 Delta mutant reduced substantially the Can(R) mutation rate of tsa1 Delta strain (33-fold), and to a lesser extent, of rad51 Delta strain (4-fold). Loss of Trr1 induced Yap1 nuclear accumulation and over-expression of a set of Yap1-regulated oxidoreductases with antioxidant properties that ultimately re-equilibrate intracellular redox environment, reducing substantially ROS-associated DNA damages. This trr1 Delta -induced effect was largely thioredoxin-dependent, probably mediated by oxidized forms of thioredoxins, the primary substrates of Trr1. Thioredoxin Trx1 and Trx2 were constitutively and strongly oxidized in the absence of Trr1. In trx1 Delta trx2 Delta cells, Yap1 was only moderately activated; consistently, the trx1 Delta trx2 Delta double deletion failed to efficiently rescue the viability of tsa1 Delta rad51 Delta. Finally, we showed that modulation of the dNTP pool size also influences the formation of spontaneous mutation in trr1 Delta and trx1 Delta trx2 Delta strains. We present a tentative model that helps to estimate the respective impact of ROS level and dNTP concentration in the generation of spontaneous mutations.
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| 3. |
- Sánchez, Arancha, et al.
(författare)
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Replication fork collapse and genome instability in dCMP deaminase mutant
- 2012
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Ingår i: Molecular and Cellular Biology. - Washington : American Society Microbiology. - 0270-7306 .- 1098-5549. ; 32:21, s. 4445-4454
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Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductase (RNR) and deoxycytidylate deaminase (dCMP deaminase) are pivotal allosteric enzymes required to maintain adequate pools of deoxyribonucleoside triphosphates (dNTPs) for DNA synthesis and repair. Whereas RNR inhibition slows DNA replication and activates checkpoint responses, the effect of dCMP deaminase deficiency is largely unknown. Here, we report that deleting the Schizosaccharomyces pombe dcd1(+) dCMP deaminase gene (SPBC2G2.13c) increases dCTP ∼30-fold and decreases dTTP ∼4-fold. In contrast to the robust growth of a Saccharomyces cerevisiae dcd1Δ mutant, fission yeast dcd1Δ cells delay cell cycle progression in early S phase and are sensitive to multiple DNA damaging agents, indicating impaired DNA replication and repair. DNA content profiling of dcd1Δcells differs from an RNR-deficient mutant. Dcd1 deficiency activates genome integrity checkpoints enforced by Rad3 (ATR), Cds1 (Chk2) and Chk1, and creates critical requirements for proteins involved in recovery from replication fork collapse, including the γH2AX-binding protein Brc1 and Mus81 Holliday junction resolvase. These effects correlate with increased nuclear foci of the single-stranded DNA binding protein RPA and the homologous recombination repair protein Rad52. Moreover, Brc1 suppresses spontaneous mutagenesis in dcd1Δ cells. We propose that replication forks stall and collapse in dcd1Δ cells, burdening DNA damage and checkpoint responses to maintain genome integrity.
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