Has flap endonuclease activity (PubMed:23821668), but does not seem to have exonuclease activity (PubMed:17567612 and PubMed:19000038). During DNA replication, flap endonucleases cleave the 5'-overhanging flap structure that is generated by displacement synthesis when DNA polymerase encounters the 5'-end of a downstream Okazaki fragment. Binds 2 Mg(2+) per subunit. Only one magnesium ion has a direct interaction with the protein, the other interactions are indirect. Binds 1 K(+) per subunit. The potassium ion strongly increases the affinity for DNA. Interacts with the DNA-binding proteins SSB and H-NS. Can be deleted, however double-disruptions of polA and xni are not viable, suggesting they have a redundant essential function. Belongs to the Xni family. Was initially reported (PubMed:9592142) as a 3'-5' exonuclease due to contamination of samples. This protein possesses no such activity (PubMed:17567612 and PubMed:19000038). Extended N-terminus. Extended N-terminus.