A New BRCT Binding Mode in TopBP1-BLM Helicase Interaction

Tandem BRCT domains are phophoprotein binding modules. In this issue of Structure , Sun et al. (2017) show that a single BRCT domain in TopBP1 binds tightly and specifically to phosphorylated Bloom syndrome helicase (BLM). This work reveals a novel BRCT binding mode and suggests a similar mechanism for TopBP1 interaction with 53BP1.