a Incubation of mAPE1 with 5′-FAM-labeled dsDNA substrates, including perfectly paired dsDNA (dsDNA 20 mer), dsDNA with an AP site in the middle (AP site), dsDNA with a 8-oxoguanine in the middle (8-oxoG) and dsDNA with a hypoxanthine base in the middle (I base). The endonuclease activity of mAPE1 demonstrates high specificity, only AP site containing dsDNA is incised. The NaCl salt concentration for the endonuclease activity assays is 120 mM. b In exonuclease activity assays, mAPE1 is incubated with 5′-FAM-labeled dsDNAs containing different nucleotide modification or biotin at the 3′-end, including AP site (3′-end AP site), 8-oxoG (3′-end 8-oxoG), and biotin (3′-end biotin). All the dsDNAs with different 3′-end modifications are excised by mAPE1 as the protein concentration is higher than 0.2 μM. The NaCl salt concentration for the exonuclease activity assays is 30 mM. a, b Source data are provided as a Source Data file.