Mitochondrial outer membrane GTPase that mediates mitochondrial clustering and fusion (PubMed:18799731, PubMed:20869429, PubMed:22396657, PubMed:24192653, PubMed:26214738). Mitochondrial fusion is the physical merging of mitochondria that gives rise to mitochondrial networks, and this process is counterbalanced by mitochondrial fission which fragments networks (PubMed:20869429, PubMed:22396657, PubMed:24192653). Promotes, but is not required for park recruitment to dysfunctional mitochondria (PubMed:20194754). GTP + H2O = GDP + H(+) + phosphate Interacts with Mul1. Widely expressed in embryos, accumulating in the mesoderm and endoderm during gut development. In the male germ line, it is expressed in spermatogonia, spermatocytes and early spermatids. Expressed both maternally and zygotically. Ubiquitinated by park and Mul1 (PubMed:24898855, PubMed:20194754). Ubiquitinated, probably by HUWE1, when dietary stearate (C18:0) levels are low; ubiquitination inhibits mitochondrial fusion (PubMed:26214738). Lethal at the early larval stage (L1/L2); mitochondria are fragmented and mitochondrial respiration is impaired (PubMed:26214738). RNAi-mediated knockdown is also lethal (PubMed:20869429). RNAi-mediated knockdown in specific tissues such as cardiomyocytes, muscles and larval neurons produces various phenotypes resulting from adherent, dysfunctional mitochondria (PubMed:18799731, PubMed:20869429, PubMed:22396657, PubMed:24192653). Mitochondria display characteristics such as abnormal cristae, fragmentation, elongation, decreased DNA content, increased ROS and depolarization (PubMed:20869429, PubMed:20194754, PubMed:22396657, PubMed:24192653). Mitochondria in larval muscles display increased mitochondrial flux and net velocity in both anterograde and retrograde directions (PubMed:20194754). Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family. Mitofusin subfamily.