Members of this family consist of ten beta-strands and a carboxy-terminal alpha-helix. The amino-terminal five beta-strands and the C-terminal five beta-strands adopt folds that are identical to each other. This domain is essential for the recruitment of proteins to double stranded breaks in DNA, which is mediated by interaction with methylated Lys 79 of histone H3 [1].

1: Methylated lysine 79 of histone H3 targets 53BP1 to DNA double-strand breaks. Huyen Y, Zgheib O, Ditullio RA Jr, Gorgoulis VG, Zacharatos P, Petty TJ, Sheston EA, Mellert HS, Stavridi ES, Halazonetis TD; Nature. 2004;432:406-411. PMID:15525939