Base excision repair in E. coli.
  1. A base pair mismatch is recognized by DNA glycosylase, which removes the base from the sugar, creating an apurinic/apyrimidinic (AP) site.

  2. AP endonuclease makes a cut in the phosphodiester backbone at the AP site.

  3. The gap is filled by DNA polymerase I and DNA ligase

  4. The error is corrected.