New functions of Ctf18-RFC in preserving genome stability outside its role in sister chromatid cohesion

Autor: Danae Schulz, Robert S. Lahue, Catherine H. Freudenreich, Lionel Gellon, Lauren Verra, David F. Razidlo, Olive Gleeson
Jazyk: angličtina
Rok vydání: 2011
Předmět:
Genome instability
Cancer Research
Saccharomyces cerevisiae Proteins
DNA Repair
lcsh:QH426-470
DNA repair
DNA damage
Cell Cycle Proteins
Saccharomyces cerevisiae
Biology
Chromatids
Genomic Instability
03 medical and health sciences
0302 clinical medicine
Replication factor C
Chromosome Segregation
Genetics
Replication Protein C
Molecular Biology
Genetics (clinical)
Ecology
Evolution
Behavior and Systematics
030304 developmental biology
Molecular Biology/DNA Replication
Molecular Biology/Recombination
0303 health sciences
Molecular Biology/DNA Repair
DNA replication
Intracellular Signaling Peptides and Proteins
Establishment of sister chromatid cohesion
Genetics and Genomics/Chromosome Biology
Genetics and Genomics/Gene Function
lcsh:Genetics
Genetics and Genomics/Disease Models
Mutation
Chromatid
Trinucleotide repeat expansion
Carrier Proteins
Trinucleotide Repeat Expansion
030217 neurology & neurosurgery
Research Article
DNA Damage
Zdroj: PLoS Genetics, Vol 7, Iss 2, p e1001298 (2011)
PLoS Genetics
ISSN: 1553-7404
1553-7390
Popis: Expansion of DNA trinucleotide repeats causes at least 15 hereditary neurological diseases, and these repeats also undergo contraction and fragility. Current models to explain this genetic instability invoke erroneous DNA repair or aberrant replication. Here we show that CAG/CTG tracts are stabilized in Saccharomyces cerevisiae by the alternative clamp loader/unloader Ctf18-Dcc1-Ctf8-RFC complex (Ctf18-RFC). Mutants in Ctf18-RFC increased all three forms of triplet repeat instability—expansions, contractions, and fragility—with effect over a wide range of allele lengths from 20–155 repeats. Ctf18-RFC predominated among the three alternative clamp loaders, with mutants in Elg1-RFC or Rad24-RFC having less effect on trinucleotide repeats. Surprisingly, chl1, scc1-73, or scc2-4 mutants defective in sister chromatid cohesion (SCC) did not increase instability, suggesting that Ctf18-RFC protects triplet repeats independently of SCC. Instead, three results suggest novel roles for Ctf18-RFC in facilitating genomic stability. First, genetic instability in mutants of Ctf18-RFC was exacerbated by simultaneous deletion of the fork stabilizer Mrc1, but suppressed by deletion of the repair protein Rad52. Second, single-cell analysis showed that mutants in Ctf18-RFC had a slowed S phase and a striking G2/M accumulation, often with an abnormal multi-budded morphology. Third, ctf18 cells exhibit increased Rad52 foci in S phase, often persisting into G2, indicative of high levels of DNA damage. The presence of a repeat tract greatly magnified the ctf18 phenotypes. Together these results indicate that Ctf18-RFC has additional important functions in preserving genome stability, besides its role in SCC, which we propose include lesion bypass by replication forks and post-replication repair.
Author Summary DNA trinucleotide repeats are naturally occurring runs of three base-pairs. Genetic mutations that expand (lengthen) triplet repeats cause multiple neurological diseases, including Huntington's disease. Triplet repeats also contract (shorten) and break. This complex behavior suggests triplet repeats are problematic for DNA replication and repair enzymes. Here, we identified a cellular factor called Ctf18-RFC that helps yeast cells accurately replicate triplet repeats. We found that mutants lacking Ctf18-RFC show enhanced levels of expansions, contractions, and fragility over a wide range of triplet repeat lengths. Other labs showed that Ctf18-RFC helps replicated chromosomes stay together until mitosis, a process called sister chromatid cohesion. However, we found that Ctf18-RFC stabilizes triplet repeats in a different way, by helping the DNA replication machinery move through triplet repeats and by helping repair any resulting DNA damage. Another insight is that Ctf18-RFC provides these functions at other sites besides triplet repeats, but the presence of a triplet repeat makes the yeast cell especially dependent on Ctf18-RFC to prevent DNA damage and allow normal cell cycle progression. Our results implicate Ctf18-RFC as a new player in the triplet repeat story and indicate that it functions through novel roles to preserve genome integrity.
Databáze: OpenAIRE
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