FIG. 1.

Mapping of a 53BP1 region required for efficient IR-induced focus formation. (A) Diagram of the human 53BP1 protein. The boundaries of the tandem tudor and BRCT domains are indicated. The oligomerization domain (OLIG) and the region C terminal to the tudor domain (RCTD) are also indicated (see below). The polypeptide corresponding to amino acids 1220 to 1711 is recruited to sites of DNA DSBs as efficiently as full-length 53BP1. (B to E) Focus-forming activities of GFP-53BP1 fusion proteins containing the indicated residues of human 53BP1. In panels C and E, all deletions were in the context of a polypeptide fragment spanning residues 1231 to 1711 of human 53BP1. The recruitment to IR-induced foci was classified as follows: wild type (+), strong foci with almost no diffuse nucleoplasmic staining; partial (/), visible foci but also clear diffuse nucleoplasmic staining; and none (−), no visible foci. (F) Sequence conservation of residues 1251 to 1271 of human 53BP1. Above the human sequence, the residues that were substituted are indicated by a / or −, depending on whether the substitution compromised or abolished focus formation. 53BP1_hs, Homo sapiens 53BP1; Crb2_sp, S. pombe Crb2; Rad9_ce, Caenorhabditis elegans Rad9; Rad9_sc, S. cerevisiae Rad9. (G) Focus-forming activities of GFP-53BP1 fusion proteins containing residues 1231 to 1711 of human 53BP1 and the indicated amino acid substitutions.