The BER pathway.BER is initiated by a damage-specific DNA glycosylase that excises the damagedbase to create an abasic site. This is incised by APE1 to create a DNA SSBharbouring a 5′-deoxyribose phosphate (5′-dRP) residue.
Pol? removes the 5′-dRPmoiety and also adds a single nucleotide into the one-nucleotide gap. Finally,XRCC1–Lig III complex seals the remaining DNA ends to complete the short-patchBER pathway (left branch). However, if the 5′-dRP is resistant to cleavage byPol?, then Pol ?/? adds 2–8 more nucleotides into the repair gap, generating a5′-flap structure that is removed by FEN-1 in a PCNA-dependent manner. Lig Ithen seals the remaining DNA ends to complete the long-patch BER pathway (rightbranch). DNA Repair (Amst). 2013May 1;12(5):326-33. Reproduced with permission from Elsevier.
Copyright ©2013DNAglycosylases scan the DNA for damaged bases. When detected, the repairglycosylase flips the damaged base into the active site pocket and thencatalyzes its removal 22. Thismechanism is carried out by both mono- and bifunctional glycosylases. Thelatter cleave the DNA backbone via an additional 3′ AP lyase activity, whichcatalyzes either ?- or ?d-eliminationreactions yielding replication and ligation blocking lesions, 3′ ?,?unsaturated aldehyde (3′-PUA), or 3′-P respectively (illustrated in Figure3). Due to differences in substrate affinities among end processors, thetype of damaged 3′ end dictates which end processor is to be involved (see Figure4 for illustration of different damaged ends and dedicated endprocessors). Usually, APE1 catalyzes the removal of 3′-PUA whereas 3′-P endsare removed by PNKP 9. Thestrand incision activity of APE1 results in the formation of 5′ deoxyribosephosphate (5’dRP) termini, which are removed via the 5’dRPase action of DNA Pol? 26restoring the 5’P.