Gap filling

DNA base excision repair is a multistep process that fixes damage to and loss of DNA bases. Base excision repair is initiated when a DNA glycosylase recognizes and cleaves the N-glycosylic bond that links the base to the phosphodiester backbone. Next the AP endonuclease cleaves the DNA backbone and removes someneighboring nucleotides. Finally, the gap is filled and sealed by DNA polymerase I and DNA ligase.