Endonuclease for the repair of UV-irradiated DNA. Involved in the excision of cyclobutane pyrimidine dimers (CPD) and 6-4 pyrimidine pyrimidones (6-4PP) which forms the UV damage repair (UVDR) pathway. Functions also in oxidative damage repair in vivo. Provides back-up AP endonuclease activity to apn2 together with apn1. By UV light. Belongs to the uve1/UvsE family.