title: A nitrate-induced frq-less oscillator in Neurospora crassa.
abstract: When nitrate is the only nitrogen source, Neurospora crassa's nitrate reductase (NR) shows endogenous oscillations in its nitrate reductase activity (NRA) on a circadian time scale. These NRA oscillations can be observed in darkness or continuous light conditions and also in a frq(9) mutant in which no functional FRQ protein is formed. Even in a white-collar-1 knockout mutant, NRA oscillations have been observed, although with a highly reduced amplitude. This indicates that the NRA oscillations are not a simple output rhythm of the white-collar-driven frq oscillator but may be generated by another oscillator that contains the nit-3 autoregulatory negative feedback loop as a part. In this negative feedback loop, a product in the reaction chain catalyzed by nitrate reductase, probably glutamine, induces repression of the nitrate reductase gene and thus downregulates its own production. This is the first example of an endogenous, nutritionally induced daily rhythm with known molecular components that is observed in the absence of an intact FRQ protein.
authors.affiliation: Stavanger University College, School of Science and Technology, Stavanger, Norway.
authors.forename: Melinda K
authors.initials: MK
authors.lastname: Christensen
authors.forename: Grete
authors.initials: G
authors.lastname: Falkeid
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Loros
authors.forename: Jay C
authors.initials: JC
authors.lastname: Dunlap
authors.forename: Cathrine
authors.initials: C
authors.lastname: Lillo
authors.forename: Peter
authors.initials: P
authors.lastname: Ruoff
mesh_terms: D003624:Darkness; D005656:Fungal Proteins / Q000235:genetics*; D009154:Mutation; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009566:Nitrates / Q000502:physiology*
chemical_list: C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D009566:Nitrates; D009565:Nitrate Reductases; D050901:Nitrate Reductase