DNA ase (or deoxyribonuclease) or simply nuclease is an enzyme which breaks down DNA by hydrolysis of the phosphodiester bonds of its sugar-phosphate back-bone. Depending on the position of hydrolysing phosphodiester bonds, nucleases are of two types:
(i) Endonucleases (ii)Exonucleases.
Endonucleases hydrolyse internal phosphodiester bonds in a polynucleotide chain (i.e., DNA). While exonucleases hydrolyse terminal phosphodiester bonds in a polynucleotide chain (i.e., DNA).