The role of break-induced replication in large-scale expansions of (CAG)n/(CTG)n repeats.

ABSTRACT: Expansions of (CAG)n/(CTG)n trinucleotide repeats are responsible for over a dozen neuromuscular and neurodegenerative disorders. Large-scale expansions are commonly observed in human pedigrees and may be explained by iterative small-scale events such as strand slippage during replication or repair DNA synthesis. Alternatively, a distinct mechanism may lead to a large-scale repeat expansion as a single step. To distinguish between these possibilities, we developed a novel experimental system specifically tuned to analyze large-scale expansions of (CAG)n/(CTG)n repeats in Saccharomyces cerevisiae. The median size of repeat expansions was ?60 triplets, although we also observed additions of more than 150 triplets. Genetic analysis revealed that Rad51, Rad52, Mre11, Pol32, Pif1, and Mus81 and/or Yen1 proteins are required for large-scale expansions, whereas proteins previously implicated in small-scale expansions are not involved. From these results, we propose a new model for large-scale expansions, which is based on the recovery of replication forks broken at (CAG)n/(CTG)n repeats via break-induced replication.

SUBMITTER: Kim JC 

PROVIDER: S-EPMC5215974 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature