This gene encodes a nuclear protein that is involved in V(D)J recombination and DNA repair. The protein has single-strand-specific 5'-3' exonuclease activity; it also exhibits endonuclease activity on 5' and 3' overhangs and hairpins when complexed with protein kinase, DNA-activated, catalytic polypeptide. Mutations in this gene cause Athabascan-type severe combined immunodeficiency (SCIDA). [provided by RefSeq, Jul 2008]