I-SceI

I-SceI was one of the first identified homing endonucleases, and is today the most widely used for research and genome engineering. I-SceI is a homing endonuclease of the LAGLIDADG family.

I-SceI was discovered by the group of Bernard Dujon in the eighties. It is encoded by the w intron of Saccharomyces cerevisiae (baker’s yeast) mitochondria. This intron was found in the large rRNA gene in a number of strains, but not in others. When intron minus strains are crossed with intron-plus strains, the intron spreads into the intronless copies of the gene by a gene conversion process, with a coconversion of the flanking exons extending over a few hundred base pairs. This conversion is initiated by the endonuclease activity of I-SceI : I-SceI delivers a DSB in the intronless copies of the genes, which is repaired by homologous recombination with the copy containing the intron.

The I-SceI DNA target site is an 18 bp sequence. On a random basis, such sequence are found once in 70 billion base pairs (4¹⁸). This specificity makes I-SceI an ideal tool for genome engineering in any organism.

Since, I-SceI has become a paradigm for meganuclease induced-recombination, and has been used to induce recombination in bacteria, yeast, mammalian cells, fish, worm, flies and plants.