Base Excision Repair

DNA bases that have been modified by the addition or loss of a small chemical group as described above are repaired by the BER pathway (Figure 3). The BER pathway begins with the excision of a damaged base by an enzyme called DNA glycosylase (Figure 3, step 1). DNA glycosylases bind to chemically altered (damaged) bases and catalyze the cleavage (hydrolysis) of the


Figure 3. Schematic diagram of the base excision repair pathway. The damaged base (in this case, guanine) is removed by a glycosylase enzyme. This creates an AP-site, which is recognized and cleaved by AP-endonuclease. DNA polymerase fills in the gap. DNA ligase links the broken strand together again.

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