Browsing by Author "Resnick, Michael A."

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    Break-Induced Replication is a Source of Mutation Clusters Underlying Kataegis
    (Elsevier B.V., 2014-06) Sakofsky, Cynthia J.; Roberts, Steven A.; Malc, Ewa; Mieczkowski, Piotr A.; Resnick, Michael A.; Gordenin, Dmitry A.; Malkova, Anna; Department of Biology, School of Science
    Clusters of simultaneous multiple mutations can be a source of rapid change during carcinogenesis and evolution. Such mutation clusters have been recently shown to originate from DNA damage within long single-strand (ss) DNA formed at resected double-strand breaks and dysfunctional replication forks. We identify here double-strand break (DSB)-induced replication (BIR) as another powerful source of mutation clusters that formed in nearly half of wild-type yeast cells undergoing BIR in the presence of alkylating damage. Clustered mutations were primarily formed along the track of DNA synthesis and were frequently associated with additional breakage and rearrangements. Moreover, the base specificity, strand coordination and strand bias of the mutation spectrum was consistent with mutations arising from damage in persistent ssDNA stretches within unconventional replication intermediates. Together, these features closely resemble kataegic events in cancers, suggesting that replication intermediates during BIR may be the most prominent source of mutation clusters across species.
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    RAD50 Is Required for Efficient Initiation of Resection and Recombinational Repair at Random, y-Induced Double-Strand Break Ends
    (PLOS, 2009-09-18) Westmoreland, Jim; Ma, Wenjian; Yan, Yan; Van Hulle, Kelly; Malkova, Anna; Resnick, Michael A.; Biology, School of Science
    Resection of DNA double-strand break (DSB) ends is generally considered a critical determinant in pathways of DSB repair and genome stability. Unlike for enzymatically induced site-specific DSBs, little is known about processing of random “dirty-ended” DSBs created by DNA damaging agents such as ionizing radiation. Here we present a novel system for monitoring early events in the repair of random DSBs, based on our finding that single-strand tails generated by resection at the ends of large molecules in budding yeast decreases mobility during pulsed field gel electrophoresis (PFGE). We utilized this “PFGE-shift” to follow the fate of both ends of linear molecules generated by a single random DSB in circular chromosomes. Within 10 min after γ-irradiation of G2/M arrested WT cells, there is a near-synchronous PFGE-shift of the linearized circular molecules, corresponding to resection of a few hundred bases. Resection at the radiation-induced DSBs continues so that by the time of significant repair of DSBs at 1 hr there is about 1–2 kb resection per DSB end. The PFGE-shift is comparable in WT and recombination-defective rad52 and rad51 strains but somewhat delayed in exo1 mutants. However, in rad50 and mre11 null mutants the initiation and generation of resected ends at radiation-induced DSB ends is greatly reduced in G2/M. Thus, the Rad50/Mre11/Xrs2 complex is responsible for rapid processing of most damaged ends into substrates that subsequently undergo recombinational repair. A similar requirement was found for RAD50 in asynchronously growing cells. Among the few molecules exhibiting shift in the rad50 mutant, the residual resection is consistent with resection at only one of the DSB ends. Surprisingly, within 1 hr after irradiation, double-length linear molecules are detected in the WT and rad50, but not in rad52, strains that are likely due to crossovers that are largely resection- and RAD50-independent.