**2.1 Engineered meganuclease (MegaN)**

Meganucleases (MegaN) are endonucleases found in nature and were discovered most often in the late 1980s. Endonucleases are capable of detecting and cleaving large nucleotide sequences (ranging from 12 to 40 base pairs), which are considerably different across many genomes [13, 18]. I-SceI, a yeast mitochondrial enzyme, and I-CreI, an algal photosynthetic enzyme, are both good meganucleases. Meganucleases have been modified to recognize previous target sequences even though meganuclease receptors are still infrequent in relevant genomes. Because of the slightly longer template strand, there is more discrimination and much more minor off-target trimming. On the other hand, engineered meganucleases had a much lower utilization than some other sequential nucleases, in addition to the issue of changing meganucleases to accept novel specificities [19, 20].
