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A Nitrate-Induced frq-Less Oscillator in Neurospora crassa

Grete Falkeid

Stavanger University College, School of Science and Technology, Stavanger, Norway

Jennifer J. Loros

Departments of Biochemistry, Dartmouth Medical School, Hanover, NH, USA

Jay C. Dunlap

Departments of Genetics, Dartmouth Medical School, Hanover, NH, USA

Cathrine Lillo

Stavanger University College, School of Science and Technology, Stavanger, Norway

Peter Ruoff

Stavanger University College, School of Science and Technology, P.O. Box 8002 Ullandhaug, 4068 Stavanger, Norwaypeter.ruoff{at}tn.his.no

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. TheseNRAoscillations can be observed in darkness or continuous light conditions and also in a frq9 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 NRAoscillations are not a simple output rhythm of the whitecollar–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.

Key Words: Neurospora crassa • circadian rhythm • nitrate reductase • oscillatory feedbackloops • multiple oscillators • frq-less oscillator (FLO)

Journal of Biological Rhythms, Vol. 19, No. 4, 280-286 (2004)
DOI: 10.1177/0748730404265532


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