The function of FIS1 (fission, mitochondrial 1, ENSG00000214253) is as follows. Involved in the fragmentation of the mitochondrial network and its perinuclear clustering (PubMed:12783892, PubMed:12861026, PubMed:14996942, PubMed:23283981). Plays a minor role in the recruitment and association of the fission mediator dynamin-related protein 1 (DNM1L) to the mitochondrial surface and mitochondrial fission (PubMed:12861026, PubMed:16118244, PubMed:23283981, PubMed:23530241, PubMed:24196833). May not be essential for the assembly of functional fission complexes and the subsequent membrane scission event (PubMed:23530241, PubMed:24196833). Also mediates peroxisomal fission (PubMed:16107562). May act when the products of fission are directed toward mitochondrial homeostasis, mitophagy, or apoptosis (PubMed:24196833). Can induce cytochrome c release from the mitochondrion to the cytosol, ultimately leading to apoptosis (PubMed:12783892). {ECO:0000269|PubMed:12783892, ECO:0000269|PubMed:12861026, ECO:0000269|PubMed:14996942, ECO:0000269|PubMed:16107562, ECO:0000269|PubMed:16118244, ECO:0000269|PubMed:23283981, ECO:0000269|PubMed:23530241, ECO:0000269|PubMed:24196833}.