Rad51 strand invasion function is needed for its role in CCTG tetranucleotide DNA repeat contractions.

Myotonic Dystrophy Type 2 is a genetic disorder caused by expanded CCTG DNA repeats in the CNBP gene. By using a genetic assay in Saccharomyces cerevisiae and knocking out RAD51 , we previously found that homologous recombination is involved in large-scale CCTG repeat contractions. In this study, we measured contraction rates using the RAD51-II3A allele, which is defective in homology search and strand invasion. We found that the mean contraction rate in the RAD51-II3A strain was indistinguishable from rad51Δ , indicating that structural properties alone of the repetitive CCTG sequence cannot initiate double strand break repair by promoting strand invasion.