Meganucleases are natural proteins found in many single-celled organisms. They are highly specific “DNA scissors”. They are able to recognize their binding site by identifying a nucleic acid sequence (nucleic acids are the constituents of DNA), which contains between 12 and over 30 base pairs. This site is statistically unique in a genome. Once the DNA break has been made, the cell activates its maintenance and repair system (for example, homologous recombination). This system corrects the DNA molecule by using, for example, its twin copy (gene correction) or a similar fragment specifically introduced into the cell as a model (insertion or “knock-in”). It is the same principle as the “copy and paste” function in word processing. When a gene just needs to be inactivated rather than replaced, the broken DNA is bound and loses information, therefore the targeted gene is inactivated (known as “knock-out”).