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DNA Repair (Amst). 2011 Jan 2;10(1):102-10. doi: 10.1016/j.dnarep.2010.10.004. Epub 2010 Nov 5.

Chromosome integrity at a double-strand break requires exonuclease 1 and MRX.

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  • 1National Institute of Environmental Health Sciences, NIH, Laboratory of Molecular Genetics, Research Triangle Park, NC 27709, USA.


The continuity of duplex DNA is generally considered a prerequisite for chromosome continuity. However, as previously shown in yeast as well as human cells, the introduction of a double-strand break (DSB) does not generate a chromosome break (CRB) in yeast or human cells. The transition from DSB to CRB was found to be under limited control by the tethering function of the RAD50/MRE11/XRS2 (MRX) complex. Using a system for differential fluorescent marking of both sides of an endonuclease-induced DSB in single cells, we found that nearly all DSBs are converted to CRBs in cells lacking both exonuclease 1 (EXO1) activity and MRX complex. Thus, it appears that some feature of exonuclease processing or resection at a DSB is critical for maintaining broken chromosome ends in close proximity. In addition, we discovered a thermal sensitive (cold) component to CRB formation in an MRX mutant that has implications for chromosome end mobility and/or end-processing.

Published by Elsevier B.V.

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