DNA repair enzyme that cleaves apurinic/apyrimidinic (AP) sites and removes 3'-blocking groups present at single strand breaks of damaged DNA. Provides back-up AP endonuclease (APE) activity to apn2 together with uve1. Binds 3 Zn(2+) ions. Belongs to the AP endonuclease 2 family. Could be the product of a pseudogene. This is a truncated version of AP endonuclease 1. In strain 972 and its derivative FY527, this gene has a stop codon in position 5, which disrupts the gene coding for this protein. PubMed:21193357 shows that the truncated protein is not functional. A full sequence for apn1 can be found in strains SPK19802 (S.pombe var. kambucha), NCYC 132, NCYC 683, NCYC 936 and NCYC 2722 (PubMed:21193357). Intron retention.