Mismatch repair: Uracil DNA glycosylase

Uracil is occasionally incorporated into DNA instead of thymine. Uracil DNA glycosylase removes uracil base from the nucleotide making an AP site. AP endonuclease makes a break in the phosphodiester backbone adjacent (5’) to the AP site. DNA polymerase I binds to the break and lays down new DNA and the gap is sealed by DNA ligase.