Circadian rhythms in Neurospora crassa: the role of mitochondria.

Energy metabolism and mitochondria have been discussed with respect to their role in the circadian rhythm mechanism for some time. Numerous examples of inhibitors that affect the mitochondria of plants and animals and microorganisms are known, which cause large phase shifts in the rhythms of these organisms. Analogous studies on the role of mitochondria in the Neurospora circadian rhythm mechanism have also been reported and summarized. This communication differs from previous studies on other organisms in that it will focus on two lines of evidence derived from studies on Neurospora strains carrying mutations affecting the mitochondria. (a) Strains whose growth rate is resistant to oligomycin (oli(r)) owing to an altered protein in the F0 sector of the mitochondrial ATPase, showed no phase shifts when pulsed with oligomycin. Control strains (oli(s)) showed large phase shifts when pulsed with oligomycin. This indicates that the phase-shifting effect of oligomycin is due to the direct inhibition of the mitochondrial ATPase and not some side effect of this inhibitor. (b) In Neurospora, many different strains are known that carry mutations in the nuclear or mitochondrial genome that affect mitochondrially localized proteins. Some of these, such as oli(r), [MI-3], or cya-5, showed shorter (approximately 19-h) periods compared with the normal (21.5-h) period. Others showed little or no change in period. Those mutant strains exhibiting shorter periods also contained approximately 60% more mitochondrial protein per gram total protein in extracts compared with the normal strains. Assays of the level of a mitochondrial-specific protein, acyl carrier protein, showed that the cellular content of this protein was approximately doubled.(ABSTRACT TRUNCATED AT 250 WORDS)