Figure 2 : Simplified overviews of the base excision repair (BER) pathway and nucleotide excision
repair (NER) pathway.

(A) In BER the damaged base is first removed by DNA glycosylases after which AP endonucleases create a single
strand break. Next either one or multiple new nucleotides are synthesized by DNA polymerases in respectively
short patch and long patch BER. FEN-1 removes the DNA flap in long patch BER and ligases seal the seams
between old and newly synthesized DNA.
(B) In NER, after the damage is recognized, the DNA helix is unwound by Transcription factor II H (TFIIH). Next
incisions are made both up- and downstream of the lesion by XPG and XPF-ERCC1, after which the DNA segment
containing the lesion can be removed. The created gap is then filled with newly synthesized DNA by DNA
polymerases and sealed by DNA ligases.

Peters et al.Oncology Discovery  2014 2:3DOI : 10.7243/2052-6199-2-3