Genome-wide Screen Identifies Pathways that Govern GAA/TTC Repeat Fragility and Expansions in Dividing and Nondividing Yeast Cells

School of Biology and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Molecular cell (Impact Factor: 14.02). 09/2012; 48(2). DOI: 10.1016/j.molcel.2012.08.002
Source: PubMed


Triplex structure-forming GAA/TTC repeats pose a dual threat to the eukaryotic genome integrity. Their potential to expand can lead to gene inactivation, the cause of Friedreich's ataxia disease in humans. In model systems, long GAA/TTC tracts also act as chromosomal fragile sites that can trigger gross chromosomal rearrangements. The mechanisms that regulate the metabolism of GAA/TTC repeats are poorly understood. We have developed an experimental system in the yeast Saccharomyces cerevisiae that allows us to systematically identify genes crucial for maintaining the repeat stability. Two major groups of mutants defective in DNA replication or transcription initiation are found to be prone to fragility and large-scale expansions. We demonstrate that problems imposed by the repeats during DNA replication in actively dividing cells and during transcription initiation in nondividing cells can culminate in genome instability. We propose that similar mechanisms can mediate detrimental metabolism of GAA/TTC tracts in human cells.

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Available from: Sergei M Mirkin, Oct 07, 2015
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    • "Additionally, breakage of longer CAG tracts (79–250 repeats) are visible as physical chromosome breaks in mitosis (Freudenreich et al., 1998) and meiosis (Jankowski et al., 2000). GAA/TCC tracts and other AT-rich elements predicted to form hairpins or cruciforms also cause chromosome fragility (Kim et al., 2008; Lobachev et al., 2002; Zhang et al., 2012b), as does the ATTCT repeat unwinding element (Cherng et al., 2011 "
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