Accurate repair of non-cohesive, double strand breaks in Saccharomyces cerevisiae: enhancement by homology-assisted end-joining

Abstract

Although the joining of blunt ends in yeast by non-homologous end joining (NHEJ) is reported to be inefficient in comparison to cohesive-end joining (Boulton and Jackson, 1996), we find that efficiency varies greatly, depending on strain, growth phase and sequence. In particular, the levels of efficiency of recircularization of a plasmid linearized by non-cohesive cleavage is augmented to that of cohesive end joining if the cleavage cut site is flanked by sequences present in the genome. We call this enhancement 'homology-assisted end joining' (HAEJ), which depends on components of the NHEJ repair pathway and, in some cases, on components of the homologous recombination (HR) pathway and on Htl1 a component of the remodels structure of chromatin (RSC) complex. The homologous genome sequences are not used as templates for repair DNA synthesis, but may facilitate end-to-end collision and ligation by providing a track for guided diffusion.