Nucleases are enzymes that cut apart nucleic acids; some cut RNA, others cut DNA. Endonucleases cut RNA or DNA somewhere within the strands, as opposed to exonucleases, which cut exclusively from the ends. Some endonucleases are highly toxic to cells because they cut just about any piece of DNA they find, regardless of its sequence. Other endonucleases are highly specific and cut only certain sequences, and many more fall somewhere in the middle.
