The Histone Chaperones ASF1 and CAF-1 Promote MMS22L-TONSL-Mediated Rad51 Loading onto ssDNA during Homologous Recombination in Human Cells
- Mol Cell. 2018 Mar 1;69(5):879-892.e5. doi: 10.1016/j.molcel.2018.01.031.
- 1. Weill Cornell Medicine, Department of Pathology and Laboratory Medicine, New York, NY 10065, USA.
- 2. Graduate Institute of Natural Products, Chang Gung University, Taoyuan 333, Taiwan.
- 3. Weill Cornell Medicine, Department of Pathology and Laboratory Medicine, New York, NY 10065, USA. Electronic address: [email protected].
The access-repair-restore model for the role of chromatin in DNA repair infers that chromatin is a mere obstacle to DNA repair. However, here we show that blocking chromatin assembly, via knockdown of the histone chaperones ASF1 or CAF-1 or a mutation that prevents ASF1A binding to histones, hinders RAD51 loading onto ssDNA during homologous recombination. This is a consequence of reduced recruitment of the RAD51 loader MMS22L-TONSL to ssDNA, resulting in persistent RPA foci, extensive DNA end resection, persistent activation of the ATR-Chk1 pathway, and cell cycle arrest. In agreement, histones occupy ssDNA during DNA repair in yeast. We also uncovered DNA-PKcs-dependent DNA damage-induced ASF1A phosphorylation, which enhances chromatin assembly, promoting MMS22L-TONSL recruitment and, hence, RAD51 loading. We propose that transient assembly of newly synthesized histones onto ssDNA serves to recruit MMS22L-TONSL to efficiently form the RAD51 nucleofilament for strand invasion, suggesting an active role of chromatin assembly in homologous recombination.