Figure 5.

BRCT-domain classes in TopBP1 and other BRCT domain proteins. (A) Array of the linkers connecting consecutive BRCT domains in structurally characterized tandem BRCT proteins. The linker segments in the triple-BRCT structure of TopBP1(1–290) are substantially shorter, resulting in the novel non-canonical domain arrangement. (B) Assignment of BRCT domain classes in TopBP1. Domains 1, 2, 3, 5 and 7 show the characteristics of phosphopeptide binding, but only BRCT7:8 resemble the canonical tandem pair arrangement found in checkpoint mediators such as Crb2, BRCA1, etc.