Mutations That Affect Circadian Rhythms in Neurospora crassa Can Alter the Reduction of Cytochromes by Blue Light

Abstract

We have examined membrane fractions from mutant strains of Neurospora crassa that have altered responses to blue light or have altered circadian rhythms. Using an in vitro assay, we assessed whether the mutations affected the levels of photoreducible cytochromes. Three of the mutant strains, prd-1, rib-1, and wc-1, were not qualitatively different from the wild type. The poky strain was found to have high concentrations of photoreducible cytochrome c. After removal of this cytochrome, however, the photoreducible cytochromes in the plasma membrane and endoplasmic reticulum were also similar to those of the wild type.

The most significant differences were found in strains mutated at the frq locus, which affects circadian rhythms. In the frq-9 strain, the cytochrome in the endoplasmic reticulum was not detectably reduced by blue light. The frq-1 mutation caused a significant shift in the spectrum of blue-light- reduced cytochrome in the endoplasmic reticulum.