ATM Localization and Heterochromatin Repair Depend on Direct Interaction of the 53BP1-BRCT2 Domain with γH2AX

Summary 53BP1 plays multiple roles in mammalian DNA damage repair, mediating pathway choice and facilitating DNA double-strand break repair in heterochromatin. Although it possesses a C-terminal BRCT2 domain, commonly involved in phospho-peptide binding in other proteins, initial recruitment of 53BP1 to sites of DNA damage depends on interaction with histone post-translational modifications—H4K20me2 and H2AK13/K15ub—downstream of the early γH2AX phosphorylation mark of DNA damage. We now show that, contrary to current models, the 53BP1-BRCT2 domain binds γH2AX directly, providing a third post-translational mark regulating 53BP1 function. We find that the interaction of 53BP1 with γH2AX is required for sustaining the 53BP1-dependent focal concentration of activated ATM that facilitates repair of DNA double-strand breaks in heterochromatin in G1.
Graphical Abstract
Highlights • The BRCT2 domain of 53BP1 binds the DNA damage chromatin mark γH2AX • Crystal structure of γH2AX bound to 53BP1-BRCT2 reveals the basis of specificity • 53BP1-BRCT2 responds to γH2AX formation by DNA damage in cells • Disruption of γH2AX binding disrupts pATM foci and DSB repair in heterochromatin
Baldock et al. find that the BRCT2 domain of 53BP1 specifically recognizes γH2AX, the primary chromatin mark at DNA double-strand breaks. Mutational disruption of this recognition in cells affects pATM recruitment into foci in G1 and results in a defect in repair of DNA damage in heterochromatin.