Fig. 3
From: DNA damage repair in ovarian cancer: unlocking the heterogeneity
The Base Excision Repair Pathway. BER consists of 5 stages: Damaged bases are recognised and removed by BER glycolases to produce an abasic intermediate. BER endonucleases (commonly APE1) make a site incision, generating a SSB. The sugar backbone is modified by phosphodiesterase. The newly formed nucleotide gap is filled by DNA polymerase. DNA ligase seals the nucleotide patch together. In SP-BER DNA polymerase B (Pol β) replaces the damaged nucleotide and the ends are ligated by DNA Lig III [58]. In LP-BER the patch is processed by proliferating cell nuclear antigen (PCNA), 9–1-1 complex and flap endonuclease 1 (FEN1), the nucleotides replaced by Pol δ and Pol ε with ligation by Lig I. in the single strand break repair (SSBR) pathway, PARP1 senses nicks in DNA, recruits XRCC1which acts as a scaffold for the other BER components to stabilise the SSB