Document Detail

Double-strand break repair pathways protect against CAG/CTG repeat expansions, contractions and repeat-mediated chromosomal fragility in Saccharomyces cerevisiae.
MedLine Citation:
PMID:  19901069     Owner:  NLM     Status:  MEDLINE    
Trinucleotide repeats can form secondary structures, whose inappropriate repair or replication can lead to repeat expansions. There are multiple loci within the human genome where expansion of trinucleotide repeats leads to disease. Although it is known that expanded repeats accumulate double-strand breaks (DSBs), it is not known which DSB repair pathways act on such lesions and whether inaccurate DSB repair pathways contribute to repeat expansions. Using Saccharomyces cerevisiae, we found that CAG/CTG tracts of 70 or 155 repeats exhibited significantly elevated levels of breakage and expansions in strains lacking MRE11, implicating the Mre11/Rad50/Xrs2 complex in repairing lesions at structure-forming repeats. About two-thirds of the expansions that occurred in the absence of MRE11 were dependent on RAD52, implicating aberrant homologous recombination as a mechanism for generating expansions. Expansions were also elevated in a sae2 deletion background and these were not dependent on RAD52, supporting an additional role for Mre11 in facilitating Sae2-dependent hairpin processing at the repeat. Mre11 nuclease activity and Tel1-dependent checkpoint functions were largely dispensable for repeat maintenance. In addition, we found that intact homologous recombination and nonhomologous end-joining pathways of DSB repair are needed to prevent repeat fragility and that both pathways also protect against repeat instability. We conclude that failure of principal DSB repair pathways to repair breaks that occur within the repeats can result in the accumulation of atypical intermediates, whose aberrant resolution will then lead to CAG expansions, contractions, and repeat-mediated chromosomal fragility.
Rangapriya Sundararajan; Lionel Gellon; Rachel M Zunder; Catherine H Freudenreich
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2009-11-09
Journal Detail:
Title:  Genetics     Volume:  184     ISSN:  1943-2631     ISO Abbreviation:  Genetics     Publication Date:  2010 Jan 
Date Detail:
Created Date:  2010-01-11     Completed Date:  2010-03-30     Revised Date:  2011-05-25    
Medline Journal Info:
Nlm Unique ID:  0374636     Medline TA:  Genetics     Country:  United States    
Other Details:
Languages:  eng     Pagination:  65-77     Citation Subset:  IM    
Program in Genetics, Sackler School of Biomedical Sciences, Tufts University, Boston, Massachusetts 02111, USA.
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MeSH Terms
Base Sequence
Cell Cycle / genetics
Chromosome Fragility / genetics*
DNA Breaks, Double-Stranded*
DNA Repair*
DNA Repeat Expansion / genetics*
Inverted Repeat Sequences
Recombination, Genetic
Saccharomyces cerevisiae / cytology,  genetics*,  metabolism
Saccharomyces cerevisiae Proteins / metabolism
Grant Support
Reg. No./Substance:
0/Saccharomyces cerevisiae Proteins
Erratum In:
Genetics. 2011 Apr;187(4):1245

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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