APE1 cleaves the phosphodiester chain 5’ to the AP site. The DNA strand then contains a 3’-hydroxyl group and a 5’-abasic deoxyribose phosphate. DNA polymerase ß (Polß) inserts the correct nucleotide based on the corresponding W-C pairing and removes the deoxyribose phosphate through its associated AP-lyase activity. The presence of X-ray repair cross-complementing group.
In human cells, HR proteins include members of the MRN complex, which consist of meiotic recombination 11 (MRE11)/radiation-sensitive mutant 50 (Rad50)/Nijmegen breakage syndrome 1 (NBS1) as well as Rad51, the Rad51 paralogs (Rad51B, Rad51C, Rad51D, X-ray repair cross-complementing group 2 (XRCC2), and XRCC3), Rad54, and Rad54B . Proteins involved in the NHEJ pathway include Ku70/80, the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), ligase IV (Lig4), XRCC4 and Artemis .