The PAS Protein VIVID Defines a Clock-Associated Feedback Loop that Represses Light Input, Modulates Gating, and Regulates Clock Resetting

vvd, a gene regulating light responses in Neurospora, encodes a novel member of the PAS/LOV protein superfamily. VVD defines a circadian clock–associated autoregulatory feedback loop that influences light resetting, modulates circadian gating of input by connecting output and input, and regulates light adaptation. Rapidly light induced, vvd is an early repressor of light-regulated processes. Further, vvd is clock controlled; the clock gates light induction of vvd and the clock gene frq so identical signals yield greater induction in the morning. Mutation of vvd severely dampens gating, especially of frq, consistent with VVD modulating gating and phasing light-resetting responses. vvd null strains display distinct alterations in the phase–response curve to light. Thus VVD, although not part of the clock, contributes significantly to regulation within the Neurospora circadian system.