Role of MMM1 in maintaining mitochondrial morphology in Neurospora crassa

Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interacti on of the mitochondrial outer membrane with the actin cytoskeleton, We repo rt the cloning and characterization of MMM1 of the filamentous fungus Neuro spora crassa, an organism that uses microtubules for mitochondrial transpor t. Mutation of the mmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochon dria at all stages of the asexual life cycle, whereas actin filament-depoly merizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the oute r membrane in a receptor-dependent manner. Our findings suggest that MMM1 i s a factor of general importance for mitochondrial morphology independent o f the cytoskeletal system used for mitochondrial transport.