Nucleic Acids Research Advance Access originally published online on October 15, 2008
Nucleic Acids Research 2008 36(20):6504-6510; doi:10.1093/nar/gkn720
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Nucleic Acids Research, 2008, Vol. 36, No. 20 6504-6510
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Genome integrity, repair and replication |
Rad51 gain-of-function mutants that exhibit high affinity DNA binding cause DNA damage sensitivity in the absence of Srs2
Department of Microbiology, Columbia University Medical Center, New York, NY 10032, USA
*To whom correspondence should be addressed. Tel: +1 212 305 4793; Fax: +1 21 305 1468; Email: lss5{at}columbia.edu
Received September 10, 2008. Accepted September 30, 2008.
We previously identified several rad51 gain-of-function alleles that partially suppress the requirement for RAD55 and RAD57 in DNA repair. To gain further insight into the mechanism of action of these alleles, we compared the activities of Rad51-V328A, Rad51-P339S and Rad51-I345T with wild-type Rad51, for DNA binding, filament stability, strand exchange and interaction with the antirecombinase helicase, Srs2. These alleles were chosen because they show the highest activity in suppression of ionizing radiation sensitivity of the rad57 mutant, and Val 328 and Ile 345 are conserved in the human Rad51 protein. All three mutant proteins exhibited higher affinity for single-stranded DNA (ssDNA) and showed more robust strand exchange activity with oligonucleotide substrates than wild-type Rad51, with the Rad51-I345T and Rad51-V328A proteins displaying higher activity than Rad51-P339S. However, the Srs2 antirecombinase was able to disrupt Rad51–ssDNA complexes formed with all the mutant proteins. In vivo, the rad51-I345T mutant strain exhibited high resistance to methyl methane sulfonate that was dependent on functional SRS2. These results suggest the Srs2 translocase is able to disrupt Rad51–ssDNA complexes at stalled replication forks, but in the absence of Srs2 the enhanced DNA binding of the Rad51-I345T protein is detrimental to cell survival.
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