Endonuclease IV (Nfo) is an apurinic/apyrimidinic endonuclease that cleaves DNA at abasic sites and processes blocked 3′ termini. In probe-based RPA it is used to cleave an abasic-site probe after target-dependent hybridization, enabling real-time or end-point signal generation. It is supplied as 2000 Units (10 units/µl), stored at -20°C, and has a stated shelf life of ≥ 24 months.