Rec2 Interplay with both Brh2 and Rad51 Balances Recombinational Repair in Ustilago maydis

Abstract

Rec2 is the single Rad51 paralog in Ustilago maydis. Here, we find that Rec2 is required for radiation-induced Rad51 nuclear focus formation but that Rec2 foci form independently of Rad51 and Brh2. Brh2 foci also form in the absence of Rad51 and Rec2. By coprecipitation from cleared extracts prepared from Escherichia coli cells expressing the proteins, we found that Rec2 interacts physically not only with Rad51 and itself but also with Brh2. Transgenic expression of Brh2 in rec2 mutants can effectively restore radiation resistance, but the frequencies of spontaneous Rad51 focus formation and allelic recombination are elevated. The Dss1-independent Brh2-RPA70 fusion protein is also active in restoring radiation sensitivity of rec2 but is hyperactive to an extreme degree in allelic recombination and in suppressing the meiotic block of rec2. However, the high frequency of chromosome missegregation in meiotic products is an indicator of a corrupted process. The results demonstrate that the importance of Rec2 function is not only in stimulating recombination activity but also in ensuring that recombination is properly controlled.

We thank Lorraine Symington and Robin Holliday for helpful comments on the manuscript and Haijuan Yang, Nikola Pavletich, and Maria Jasin for continuing interest and enthusiastic discussions.

W.K.H. gratefully acknowledges financial support for this work from National Institutes of Health grant GM42482, the Department of Defense Breast Cancer Research Program grant DAMD17-3-1-0234, and the William Randolph Hearst Foundation.