Meganuclease I-Sce I is a homing endonuclease. It recognises an 18-base pair sequence TAGGGATAACAGGGTAAT and leaves a 4 base pair 3' hydroxyl overhang. It is a rare cutting endonuclease. Statistically an 18-bp sequence will occur once in every 6.9*1010 base pairs or once in 20 human genomes. [1]
I-SceI is coded by introns. It is present in the mitochondria of yeast Saccharomyces cerevisiae.