Meganucleases are found in a large number of organisms – Archaea or archaebacteria, bacteria, phages, fungi, yeast, algae and some plants.
Introns propagate by intervening at a precise location in the DNA, where the expression of the meganuclease produces a break in the complementary intron- or intein-free allele.
The best characterized endonucleases which are most widely used in research and genome engineering include I-SceI (discovered in the mitochondria of baker's yeast Saccharomyces cerevisiae), I-CreI (from the chloroplasts of the green algae Chlamydomonas reinhardtii) and I-DmoI (from the archaebacterium Desulfurococcus mobilis).
The best known LAGLIDADG endonucleases are homodimers (for example I-CreI, composed of two copies of the same protein domain) or internally symmetrical monomers (I-SceI).
The half-binding sites can be extremely similar and bind to a palindromic or semi-palindromic DNA sequence (I-CreI), or they can be non-palindromic (I-SceI).
Meganucleases were identified in the 1990s, and subsequent work has shown that they are particularly promising tools for genome engineering and gene editing, as they are able to efficiently induce homologous recombination,[2] generate mutations,[3] and alter reading frames.
Precision Biosciences, another biotechnology company, has developed a fully rational design process called Directed Nuclease Editor (DNE) which is capable of creating engineered meganucleases that target and modify a user-defined location in a genome.
[12] In 2012 researchers at Bayer CropScience used DNE to incorporate a gene sequence into the DNA of cotton plants, targeting it precisely to a predetermined site.
[13] One recent advance in the use of meganucleases for genome engineering is the incorporation of the DNA binding domain from transcription activator-like (TAL) effectors into hybrid nucleases.
[14] In addition, meganucleases have been fused to DNA end-processing enzymes in order to promote error-prone non-homologous end joining[15] and to increase the frequency of mutagenic events at a given locus.