The Rad51 Paralog Rad51B Promotes Homologous Recombinational Repair

Abstract

The highly conserved Saccharomyces cerevisiae Rad51 protein plays a central role in both mitotic and meiotic homologous DNA recombination. Seven members of the Rad51 family have been identified in vertebrate cells, including Rad51, Dmc1, and five Rad51-related proteins referred to as Rad51 paralogs, which share 20 to 30% sequence identity with Rad51. In chicken B lymphocyte DT40 cells, we generated a mutant with RAD51B/RAD51L1, a member of the Rad51 family, knocked out. RAD51B^−/− cells are viable, although spontaneous chromosomal aberrations kill about 20% of the cells in each cell cycle. Rad51B deficiency impairs homologous recombinational repair (HRR), as measured by targeted integration, sister chromatid exchange, and intragenic recombination at the immunoglobulin locus. RAD51B^−/− cells are quite sensitive to the cross-linking agents cisplatin and mitomycin C and mildly sensitive to γ-rays. The formation of damage-induced Rad51 nuclear foci is much reduced in RAD51B^−/−cells, suggesting that Rad51B promotes the assembly of Rad51 nucleoprotein filaments during HRR. These findings show that Rad51B is important for repairing various types of DNA lesions and maintaining chromosome integrity.

ACKNOWLEDGMENTS

We thank M. Hashishin, Y. Sato, O. Koga, and M. Hirao for excellent technical assistance and H. Kurumizaka and T. Shibata (Riken, Wako, Japan), S. C. West (Imperial Cancer Research Fund, South Mimms, United Kingdom), and D. Schild (Lawrence Berkeley National Laboratory, Berkeley, Calif.) for discussion and critical reading of the manuscript.

C. M. is the recipient of a JSPS postdoctoral fellowship. The Bayer-Chair Department of Molecular Immunology and Allergy is supported by Bayer Yakuhin, Kyoto, Japan. This work was supported in part by CREST, JST (Saitama, Japan); a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture of Japan; and grants from The Mochida Memorial Foundation for Medical and Pharmaceutical Research and from The Uehara Memorial Foundation. A portion of this work was prepared under the auspices of the U.S. Department of Energy under contract W-7405-ENG-48 (L.H.T.).