Intron-encoded endonuclease I-Sce I is a homing endonuclease. The enzyme is used in biotechnology as a meganuclease. 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 (a frequency of 1 in 4¹⁸). This sequence does not normally occur in a human or mouse genome.

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I-SceI is coded by introns. It is present in the mitochondria of yeast Saccharomyces cerevisiae.