Photosynchronization of the circadian clock of Schizosaccharomyces pombe: Mitochondrial cytochrome b is an essential component

Summary

Visible light exerts a dual effect on Schizosaccharomyces pombe. It synchronizes its circadian clock to a diurnal light-dark cycle. At lower temperatures it slows down, and at higher intensities eventually inhibits, growth. Screening of available mutants deficient in one or two mitochondrial cytochromes indicated involvement of these cytochromes in both effects. Mutants lacking only one cytochrome were as sensitive to light inhibition as was the wild-type. Mutants deficient in both cytochrome b and cytochrome a/a ₃ showed partial resistance to a varying degree, but growth rate of the dark control was never reached. With respect to synchronization the pattern is more clearcut. Two mutants lacking only cytochrome a/a ₃ could still be syndronized. In contrast, four different mutants lacking only cytochrome b, and four different mutants lacking both cytochrome b and cytochrome a/a ₃ , all failed to entrain to a light-dark cycle. These results demonstrate that mitochondrial cytochrome b is necessary for photosynchronization either as the primary photoreceptor or as a part of the transduction chain.