What is it about?
We investigated how the Mph1 DNA helicase in budding yeast, Saccharomyces cerevisiae, helps cells respond when DNA damage interferes with chromosome replication. We developed the KanKanMX4 reporter, a sensitive genetic system that detects repair events between sister chromatids, the paired DNA copies made during replication. Damage-induced events required homologous recombination: RAD52 was essential, RAD51 was needed for most events, and Rad30/Pol eta contributed to part of the response. Cells lacking MPH1 showed fewer damage-induced sister chromatid interactions after treatment with 4-NQO, MMS or camptothecin. Together with comparison to a second reporter system, the results suggest that Mph1 favours a gene-conversion-like route in which one DNA copy uses its sister chromatid as a template, involving strand invasion and D-loop formation or stabilisation.
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Why is it important?
DNA damage during replication can threaten genome stability, so cells need ways to continue replication while limiting errors. This work adds a useful assay for studying sister chromatid interactions in yeast and supports the idea that Mph1 acts in an error-free pathway for bypassing replication-blocking DNA lesions. It also suggests that Mph1 has a constructive role in recombination intermediates, which may help explain why loss of Mph1 affects both mutation patterns and DNA damage responses.
Perspectives
What stands out to us is that a short duplicated KanMX4 sequence gave us a sensitive way to follow damage-induced interactions between sister chromatids. The genetic patterns were especially informative because RAD52, RAD51, RAD30, REV3 and MPH1 mutants helped separate spontaneous events, damage-induced events, translesion synthesis and recombination-mediated repair. We find this publication useful because it gives a more nuanced view of Mph1: not only as a protein that can disrupt D-loops, but also as one that appears to help form or process the DNA pairing structures needed for repair.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Budding yeast Mph1 promotes sister chromatid interactions by a mechanism involving strand invasion, DNA Repair, January 2011, Elsevier,
DOI: 10.1016/j.dnarep.2010.09.009.
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