Regulation of Cyanide‐Insensitive Respiration in Neurospora

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Abstract
Inhibition of either mitochondrial transcription or translation in N. crassa results in the rapid production of the cyanide-insensitive pathway of mitochondrial respiration. Protein synthesis on cytoplasmic ribosomes is required for the appearance of cyanide-insensitive respiration in the culture. Removal of the inhibition of transcription or translation results in a rapid return to cyanide-sensitive respiration. Additional protein synthesis in the cytoplasm is required for the loss of cyanide-insensitive respiratory activity while additional mitochondrial protein synthesis has no effect. A mitochondrial gene product apparently is involved in a negative manner in the regulation of cyanide-insensitive respiration. When the mitochondrial product is present, the pathway is not expressed; when the mitochondrial product is absent, the pathway is expressed. Studies with forced heterokaryons formed from respiratory-deficient mutants having cyanide-insensitive respiration and respiratory-competent auxotrophs indicate that the site of action of the mitochondrial gene product is external to the mitochondrion.