Light and clock expression of the Neurospora clock gene frequency is differentially driven by but dependent on WHITE COLLAR-2.
Visible light is thought to reset the Neurospora circadian clock by acting through heterodimers of the WHITE COLLAR-1 and WHITE COLLAR-2 proteins to induce transcription of the frequency gene. To characterize this photic entrainment we examined frq expression in constant light, under which condition the mRNA and protein of this clock gene were strongly induced. In continuous illumination FRQ accumulated in a highly phosphorylated state similar to that seen at subjective dusk, the time at which a step from constant light to darkness sets the clock. Examination of frq expression in several wc-2 mutant alleles surprisingly revealed differential regulation when frq expression was compared between constant light, following a light pulse, and darkness (clock-driven expression). Construction of a wc-2 null strain then demonstrated that WC-2 is absolutely required for both light and clock-driven frq expression, in contrast to previous expectations based on presumptive nulls containing altered Zn-finger function. Additionally, we found that frq light signal transduction differs from that of other light-regulated genes. Thus clock and light-driven frq expression is differentially regulated by, but dependent on, WC-2.
Collett
Michael A
MA
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Garceau
Norm
N
Dunlap
Jay C
JC
Loros
Jennifer J
JJ
D002940:Circadian Rhythm / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000502:physiology*; D003624:Darkness; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal / Q000528:radiation effects; D005787:Gene Frequency; D008027:Light; D009492:Neurospora crassa / Q000737:chemistry / Q000235:genetics*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000502:physiology*; D016335:Zinc Fingers / Q000502:physiology
D004268:DNA-Binding Proteins; C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D014157:Transcription Factors; C103772:white collar 2 protein, Neurospora