Fragile DNA Motifs Trigger Mutagenesis at Distant Chromosomal Loci in Saccharomyces cerevisiae

Dna sequences capable of adopting non-canonical secondary structures have been associated with gross-chromosomal rearrangements in humans and model organisms. previously,we have shown that long inverted repeats that form hairpin and cruciform structures and triplex-forming gaa/ttc repeats induce the formation of double-strand breaks which trigger genome instability in yeast. in this study,we demonstrate that breakage at both inverted repeats and gaa/ttc repeats is augmented by defects in dna replication. increased fragility is associated with increased mutation levels in the reporter genes located as far as 8 kb from both sides of the repeats. the increase in mutations was dependent on the presence of inverted or gaa/ttc repeats and activity of the translesion polymerase polζ. mutagenesis induced by inverted repeats also required sae2 which opens hairpin-capped breaks and initiates end resection. the amount of breakage at the repeats is an important determinant of mutations as a perfect palindromic sequence with inherently increased fragility was also found to elevate mutation rates even in replication-proficient strains. we hypothesize that the underlying mechanism for mutagenesis induced by fragile motifs involves the formation of long single-stranded regions in the broken chromosome,invasion of the undamaged sister chromatid for repair,and faulty dna synthesis employing polζ. these data demonstrate that repeat-mediated breaks pose a dual threat to eukaryotic genome integrity by inducing chromosomal aberrations as well as mutations in flanking genes. © 2013 saini et al.