Role of DNA Polymerases in Repeat-Mediated Genome Instability

• Published in: Cell reports (Cambridge) 2012-11, Vol.2 (5), p.1088-1095
• Main Authors: Shah, Kartik A., Shishkin, Alexander A., Voineagu, Irina, Pavlov, Youri I., Shcherbakova, Polina V., Mirkin, Sergei M.
• Format: Article
• Language: English
• Subjects: DNA - genetics; DNA Polymerase I - genetics; DNA Polymerase I - metabolism; DNA Polymerase II - genetics; DNA Polymerase II - metabolism; DNA Polymerase III - genetics; DNA Polymerase III - metabolism; Genomic Instability; Introns; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Statistics, Nonparametric; Trinucleotide Repeat Expansion
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2012.10.006

Expansions of simple DNA repeats cause numerous hereditary diseases in humans. We analyzed the role of DNA polymerases in the instability of Friedreich’s ataxia (GAA)n repeats in a yeast experimental system. The elementary step of expansion corresponded to ∼160 bp in the wild-type strain, matching the size of Okazaki fragments in yeast. This step increased when DNA polymerase α was mutated, suggesting a link between the scale of expansions and Okazaki fragment size. Expandable repeats strongly elevated the rate of mutations at substantial distances around them, a phenomenon we call repeat-induced mutagenesis (RIM). Notably, defects in the replicative DNA polymerases δ and ε strongly increased rates for both repeat expansions and RIM. The increases in repeat-mediated instability observed in DNA polymerase δ mutants depended on translesion DNA polymerases. We conclude that repeat expansions and RIM are two sides of the same replicative mechanism. [Display omitted] ► Elementary step of repeat expansion corresponds to size of an Okazaki fragment ► Mutated DNA polymerase α leads to an increase in expansion step ► Mutated DNA polymerases δ and ε lead to elevated expansion rates ► Repeats induce mutagenesis, which is further elevated in polymerase mutants Expansions of simple DNA repeats cause numerous hereditary diseases in humans. In a yeast experimental system, Mirkin and colleagues analyzed the role of DNA polymerases in the instability of a repeat that is responsible for Friedreich’s ataxia in humans. They found that mutated DNA polymerases increase both repeat instability and its propensity to induce mutagenesis. They conclude that repeat expansions and repeat-mediated mutagenesis are two sides of the same replicative mechanism.