Mitochondrial biogenesis during fungal spore germination. Catalytic activity, composition, and subunit biosynthesis of oligomycin-sensitive ATPase in Botryodiplodia.

Mitochondria from dormant spores of the fungus Botryodiplodia theobromae did not contain a functional oligomycinor dicyclohexylcarbodiimide-sensitive adenosine triphosphatase (ATPase); however, this enzyme activity was elaborated rapidly after 120 min of a 240-min germination sequence. The development of oligomycin-sensitive ATPase in germinating spores was abolished by cycloheximide but initially was insensitive to inhibitors of the mitochondrial genetic system, chloramphenicol or ethidium bromide. Biosynthesis of the polypeptide subunits of the enzyme was measured through use of antisera directed against the F1-ATPase and the chloroform-methanol-soluble proteolipid of the enzyme. The immunoprecipitated enzyme consisted of at least 12 polypeptides with molecular weights ranging from 58,000-8,000. Biosynthesis studies with ribosome-specific inhibitors showed that only one polypeptide (subunit 7) of the enzyme was synthesized on mitochondrial ribosomes and that the remainder were products of cytoplasmic protein synthesis. Subunit 12 was characterized by its binding in vitro to [14C]dicyclohexylcarbodiimide, and analysis of its amino acid composition showed that the hydrophobic peptide had a polarity index of 25%. Synthesis of all enzyme subunits began together during the first 45 min of germination when little (if any) mRNA was synthesized, and this early synthesis in vivo depended upon translation of a mRNA preserved in these spores. An examination of subunit polypeptides present in the dormant spores showed that the respiration-incompetent mitochondria contained at least two or three of the cytoplasmic subunits of the enzyme and that these preserved subunits were not assembled into a complex. De novo synthesis of the absent subunit polypeptides early in germination probably is required for assembly and function of the spore mitochondrial ATPase.