Journal of Biological Chemistry
Volume 286, Issue 7, 18 February 2011, Pages 5119-5125
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DNA and Chromosomes
Homologous Recombination-dependent Rescue of Deficiency in the Structural Maintenance of Chromosomes (Smc) 5/6 Complex*

https://doi.org/10.1074/jbc.M110.201608Get rights and content
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The essential and evolutionarily conserved Smc5-Smc6 complex (Smc5/6) is critical for the maintenance of genome stability. Partial loss of Smc5/6 function yields several defects in DNA repair, which are rescued by inactivation of the homologous recombination (HR) machinery. Thus HR is thought to be toxic to cells with defective Smc5/6. Recent work has highlighted a role for Smc5/6 and the Sgs1 DNA helicase in preventing the accumulation of unresolved HR intermediates. Here we investigate how deletion of MPH1, encoding the orthologue of the human FANCM DNA helicase, rescues the DNA damage sensitivity of smc5/6 but not sgs1Δ mutants. We find that MPH1 deletion diminishes accumulation of HR intermediates within both smc5/6 and sgs1Δ cells, suggesting that MPH1 deletion is sufficient to decrease the use of template switch recombination (TSR) to bypass DNA lesions. We further explain how avoidance of TSR is nonetheless insufficient to rescue defects in sgs1Δ mutants, by demonstrating a requirement for Sgs1, along with the post-replicative repair (PRR) and HR machinery, in a pathway that operates in mph1Δ mutants. In addition, we map the region of Mph1 that binds Smc5, and describe a novel allele of MPH1 encoding a protein unable to bind Smc5 (mph160). Remarkably, mph160 supports normal growth and responses to DNA damaging agents, indicating that Smc5/6 does not simply restrain the recombinogenic activity of Mph1 via direct binding. These data as a whole highlight a role for Smc5/6 and Sgs1 in the resolution of Mph1-dependent HR intermediates.

DNA Helicase
DNA Recombination
DNA Repair
DNA Replication
DNA Topology
Mph1
Sgs1
Smc5/6

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*

This work was supported, in whole or in part, by National Institutes of Health Grants R01-AG021521 and P01-AG031862 (to F. B. J.) and T32-AG000255 (to A. C.).

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S12 and Table S1.