title: Fragile DNA motifs trigger mutagenesis at distant chromosomal loci in saccharomyces cerevisiae.
abstract: 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.
authors.affiliation: School of Biology and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, USA.
authors.forename: Natalie
authors.initials: N
authors.lastname: Saini
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yuri
authors.initials: Y
authors.lastname: Nishida
authors.forename: Ziwei
authors.initials: Z
authors.lastname: Sheng
authors.forename: Shilpa
authors.initials: S
authors.lastname: Choudhury
authors.forename: Piotr
authors.initials: P
authors.lastname: Mieczkowski
authors.forename: Kirill S
authors.initials: KS
authors.lastname: Lobachev
mesh_terms: D002869:Chromosome Aberrations; D002875:Chromosomes / Q000235:genetics*; D053903:DNA Breaks, Double-Stranded; D042822:Genomic Instability; D055029:Inverted Repeat Sequences / Q000235:genetics*; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D059372:Nucleotide Motifs / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D018911:Trinucleotide Repeats / Q000235:genetics