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  • Title: The band mutation in Neurospora crassa is a dominant allele of ras-1 implicating RAS signaling in circadian output.
    Author: Belden WJ, Larrondo LF, Froehlich AC, Shi M, Chen CH, Loros JJ, Dunlap JC.
    Journal: Genes Dev; 2007 Jun 15; 21(12):1494-505. PubMed ID: 17575051.
    Abstract:
    band, an allele enabling clear visualization of circadianly regulated spore formation (conidial banding), has remained an integral tool in the study of circadian rhythms for 40 years. bd was mapped using single-nucleotide polymorphisms (SNPs), cloned, and determined to be a T79I point mutation in ras-1. Alterations in light-regulated gene expression in the ras-1(bd) mutant suggests that the Neurospora photoreceptor WHITE COLLAR-1 is a target of RAS signaling, and increases in transcription of both wc-1 and fluffy show that regulators of conidiation are elevated in ras-1(bd). Comparison of ras-1(bd) with dominant active and dominant-negative ras-1 mutants and biochemical assays of RAS function indicate that RAS-1(bd) displays a modest enhancement of GDP/GTP exchange and no change in GTPase activity. Because the circadian clock in ras-1(bd) appears to be normal, ras-1(bd) apparently acts to amplify a subtle endogenous clock output signal under standard assay conditions. Reactive oxygen species (ROS), which can affect and be affected by RAS signaling, increase conidiation, suggesting a link between generation of ROS and RAS-1 signaling; surprisingly, however, ROS levels are not elevated in ras-1(bd). The data suggest that interconnected RAS- and ROS-responsive signaling pathways regulate the amplitude of circadian- and light-regulated gene expression in Neurospora.
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