eLife assessment
In the DNA damage response (DDR) pathway, single-stranded DNAs (ssDNAs) activate a downstream kinase cascade with ATR/Chk1. Replication protein A (RPA) is believed to be essential for DDR activation by recruiting an ATR-partner protein, ATRIP, to RPA-coated ssDNAs through direct protein-protein interaction. This important paper provides convincing results, showing that an AP endonuclease, APE1 (APEX1), plays a role not only in RPA-dependent but also in RPA-independent recruitment of ATRIP on ssDNAs for DDR activation.