Mitochondrial DNA endonuclease involved in intron homing. The mature protein may arise from proteolytic cleavage of an in-frame translation of COX1 exons 1 to 7 plus intron 7, containing the aI7 open reading frame. In the C-terminal section; belongs to the LAGLIDADG endonuclease family. In the N-terminal section; belongs to the heme-copper respiratory oxidase family.