Involved in the fragmentation of the mitochondrial network and its perinuclear clustering (PubMed:18443288, PubMed:20194754). Functions downstream of Pink1 and upstream of Drp1 to regulate mitochondrial fission (PubMed:18443288). The C-terminus is required for mitochondrial localization, while the N-terminus is necessary for mitochondrial fission. RNAi-mediated knockdown results in elongated mitochondria. Belongs to the FIS1 family.