Deoxyribonuclease I (DNase I) is an endonuclease that digests single- or double-stranded DNA. It recognizes and cleaves phosphodiester bonds to produce a single deoxynucleotide or single- or double-stranded oligodeoxynucleotide with 5′-phosphorylated and 3′-hydroxylated ends. The activity of DNase I depends on Ca2+, and DNase I can also be activated by divalent metal ions such as Mg2+ and Mn2+.