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The rad51-K191R ATPase-Defective Mutant Is Impaired for Presynaptic Filament Formation ^,

Cindy W. Fung,¹ Gary S. Fortin,^3, Shaun E. Peterson,² and Lorraine S. Symington^3*

Graduate Program in Cellular, Molecular and Biophysical Studies,¹ Graduate Program in Biological Sciences,² Department of Microbiology, Columbia University Medical Center, New York, New York 10032³

Received 6 April 2006/ Returned for modification 2 June 2006/ Accepted 3 October 2006

The nucleoprotein filament formed by Rad51 polymerization on single-stranded DNA is essential for homologous pairing and strand exchange. ATP binding is required for Rad51 nucleoprotein filament formation and strand exchange, but ATP hydrolysis is not required for these functions in vitro. Previous studies have shown that a yeast strain expressing the rad51-K191R allele is sensitive to ionizing radiation, suggesting an important role for ATP hydrolysis in vivo. The recruitment of Rad51-K191R to double-strand breaks is defective in vivo, and this phenotype can be suppressed by elimination of the Srs2 helicase, an antagonist of Rad51 filament formation. The phenotype of the rad51-K191R strain is also suppressed by overexpression of Rad54. In vitro, the Rad51-K191R protein exhibits a slight decrease in binding to DNA, consistent with the defect in presynaptic filament formation. However, the rad51-K191R mutation is dominant in heterozygous diploids, indicating that the defect is not due simply to reduced affinity for DNA. We suggest the Rad51-K191R protein either forms an altered filament or is defective in turnover, resulting in a reduced pool of free protein available for DNA binding.

Published ahead of print on 9 October 2006.

Supplemental material for this article may be found at http://mcb.asm.org/.

Present address: Abbott Laboratories, Inc., 2201 Pennsylvania Avenue, Rm. 1103, Philadelphia, PA 19130.

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