An enzyme that digests a polynucleotide chain beginning at either the 5′ (RecJ) or the 3′ terminus (Exo I, VI, X) or from both ends (ExoVII). Among these only ExoX degrades double-strand DNA. Exonucleases may degrade misaligned tandem repeats and thus favor DNA stability (Feschenko VV et al 2003 Proc Nat Acad Sci USA 100:1134).  Bal1,  recombination mechanisms,  endonuclease,  restriction enzymes,  mismatch repair,  RecA-independent recombination; Grunberg-Manago M 1999 Annu Rev Genet 33:193; Shevelev IV, Hübscher U 2002 Nature Rev Mol Cell Biol 3:364.