One of several uracil DNA glycosylases excise uracil, leaving an AP site. APE1 recognizes these sites and creates single strand breaks. POL β fills in these sites, and LIG3 seals the nick. Right: Mismatch repair can excise repair uracil from DNA. Uracil is recognized by the MSH2-MSH6 heterodimer. The MLH1-PMS3 heterodimer creates nick on either side of the uracil moiety. EXO1 degrades the nicked DNA. DNA is filled in by either POL δ or POL ε. BER = base excision repair. U, Uracil; UDG, uracil DNA glycosylase;.AP, abasicsite; APE1, AP endonuclease 1; POL β, DNA pol beta; MSH2, MutS homolog 2; MSH6, MutS homolog 6; MLH1, MutL homolog 1; PMS2, PMS1 homolog 2; EXO1, Exonuclease 1; Pol δ, DNA polymerase δ; Pol ε, DNA polymerase ε.