Mitochondrial Fission 1 Protein (FIS1) is a member of the FIS1 family. FIS1 is a single-pass membrane protein and contains one TPR repeat. FIS1 is part of the mitochondrial complex that promotes mitochondrial fission. FIS1 can induce cytochrome C discharge from the mitochondrion to the cytosol, eventually leading to apoptosis. In addition, FIS1 participates in peroxisomal growth and division. The C-terminus of FIS1 is required for mitochondrial or peroxisomal localization, while the N-terminus is necessary for mitochondrial or peroxisomal fission, localization and regulation of the interaction with DNM1L.