 APE-1 is a protein involved in the DNA damage response pathway. It was previously thought that APE-1 interacts with RPA-coated single-stranded DNA, SSDNA, but new research shows that APE-1 can also bind to RPA without being bound to SSDNA. This allows APE-1 to recruit a trip, which is necessary for the activation of the ATR check 1DDR pathway. This article was authored by Yun Feng Lin, Zhou Li, Hai Chao Chao, and others.