TETRAHYMENA INTRAMITOCHONDRIAL FILAMENTOUS INCLUSIONS CONTAIN 14-NM FILAMENT PROTEIN CITRATE SYNTHASE

Tetrahymena 14-nm filament protein has been shown to have dual functio ns as a citrate synthase in mitochondria and as a cytoskeletal protein in oral morphogenesis and pronuclear behavior during conjugation. Imm unofluorescence studies of the 14-nm filament protein/citrate synthase in mitochondria found that intense mitochondrial fluorescence remaine d unchanged in Tetrahymena cells taken from logarithmic growth phase t o stationary phase, However, electron microscopic studies showed that electron-dense rod-shaped structures found in mitochondrial matrices t ended to increase in Tetrahymena cells in the growth decline phase, Th e rods were composed of side-by-side straight filaments with diameters of approximately 14 to 16 nm, Serial sections revealed that in Tetrah ymena cells in growth decline phase, one to four electron-dense rods e xisted in the matrices of every mitochondrion, Immunoelectron microsco py using an anti-14-nm filament antibody clearly showed that a filamen t bundle of the electron-dense rod was the bundle of polymerized filam ents of 14-nm filament protein/citrate synthase, These results strongl y suggest that dynamic monomer-polymer conversion of the 14-nm filamen t protein/citrate synthase in mitochondria depends upon the physiologi cal conditions of Tetrahymena cells. (C) 1995 Academic Press, Inc.