Performs endonucleolytic cleavage at abasic sites, which are generated by the base-excision activity of host Ung (PubMed:34074772). The cleavage generates a 5'-deoxyribose phosphate and 3'-hydroxyl end (PubMed:34074772). The sites are specifically recognized through the formation of a complex with host Ung (PubMed:34074772). The viral endonucleolytic activity damages the host DNA, blocks host DNA replication and induces cell division arrest (PubMed:34074772). This may provide an advantage for the phage and save nucleotides for the viral replication since it specifically targets the host DNA, which possesses more misincorporated uracils than the viral genome (Probable). Interacts with host Ung; this interaction allows the viral AP endonuclease to localize to newly formed AP sites and cleave them, leading to inhibition of bacterial growth. Belongs to the apurinic/apyrimidinic endonuclease family.