Abstract
Chromosomal fragile sites (CFS's) are specific loci associated with a high frequency of breakage and recombination. A cell's ability to repair and/or replicate through a lesion is prerequisite to the maintenance of genomic stability. This work seeks to identify and characterize both trans and cis CFS associated elements involved in instability onset and progression. An array of S. cerevisiae isogenic DNA repair deficient mutants were utilized to identify genes contributing to the stability or instability of a natural CFS ~ 403 kb from the left telomere on chrVII. Findings suggest that the RAD52 epistasis group, MRX, NHEJ, MUS81 and SGS1, TLS polymerases, and a majority of PRR proteins are required for faithful replication of the 403 CFS, and likely other CFS's as well. In contrast, we find that MMS2 (previously thought to be specific to the PRR pathway), MGS1 (homolog of human WHIP), and POL3 (DNA pol delta subunit) promote error prone events at regions at risk of replication damage. We further find the presence of inverted repeats (IR) are sufficient to induce instability. Two IR's proximal to the 403 site consistently fuse to generate acentric and dicentric chromosomes involving the 403 CFS and a newly identified site on chrVII as well. The frequency of fusion events is aggravated by chromatin traffic stressors such as tRNA transcription induced fork stalling and replisome termination regions.
Published Version
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