Mitochondrial biogenesis during fungal spore germination: Products of mitochondrial protein synthesis in vivo

Germinated spores of the fungus Botryodiplodia theobromae synthesized about eight to ten mitochondrial proteins in the presence of cycloheximide as shown by acrylamidegel electrophoresis of [³H]leucine-labeled, detergent-solubilized mitochondrial extracts. The apparent molecular weights of these proteins (whose synthesis was blocked by chloramphenicol) ranged from 85,100 to 8400. The 8400 molecular weight protein was soluble in chloroform-methanol, while other mitochondrial proteins (including also those proteins synthesized only in the absence of cycloheximide) were insoluble in this solvent system. Treatment of intact mitochondria with trichloroacetic acid before detergent extraction caused conversion of the higher molecular weight radioactivity to the 8400 molecular weight form. Labeling kinetics of 300-min (germinated) spores indicated that the 8400 molecular weight protein was the first to contain [³H]leucine, and with increasing time of incubation the label appeared in the higher molecular weight proteins. The mitochondrial ribosomes of the spores were not active during the first 60 min of germination, although products of the cytoplasmic ribosomes were incorporated into or associated with mitochondria during this interval; during the second 60-min interval of germination, function of mitochondrial ribosomes was observed by synthesis of the 8400 molecular weight, chloroform-methanol-soluble protein. In three subsequent 60-min intervals of germination, radioactivity from [³H]leucine was incorporated into the higher molecular weight proteins. The significance of this mitochondrial protein synthesis in relation to other metabolic activities of the germinating spores is discussed.