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FRIMEDBIO-Fri med.,helse,biol

An Environmentally Induced FRQ-Independent 24 hour Rhythm in Neurospora crassa

Awarded: NOK 1.8 mill.

Circadian rhythms (from latin circa, about; and dies, day) play an important role in the adaptation of organisms to their natural environment. It is assumed that by measuring day length, the circadian clock participates in the initiation of important dail y processes, for example sleep or activity rhythms as well as in the induction of seasonal processes such as flower induction, migration of birds and certain butterflies, or hibernation. Genetic studies in the model organisms Neurospora, Drosophila, or mo use have provided important contributions that have been crucial to understand the molecular components of the circadian clock. The frequency (frq) gene is considered to be a central element in the circadian pacemaker of Neurospora crassa’s biological clo ck. We have found a new self-sustained 24 h rhythm in Neurospora’s nitrate reductase activity (NRA), which can be observed in constant darkness or constant light. This rhythm is only observed when the growth medium contains nitrate ions as the sole nitrog en source. Interestingly, the NRA rhythm can be also observed in the frq9 mutant, which has no functional FRQ protein. The NRA oscillations can be understood as the result of a negative feedback loop where glutamine, a product in the reaction sequence cat alyzed by nitrate reductase (NR) inhibits - via the “nitrogen metabolite repression” (NMR) protein - transcription of nit-3, the structural gene of NR. In this project we wish to investigate by means of molecular biology and genetic techniques to what ext ent the NR rhythm meets the requirements for being circadian, how the putative components of the NR oscillator vary in time and what effects temperature or light have on nit-3 transcription rates, mRNA levels, or NR protein levels. By using Neurospora mut ants we also wish to investigate whether frq and the NR oscillator interact and whether the NR negative feedback loop is necessary to generate the NR oscillations.

Funding scheme:

FRIMEDBIO-Fri med.,helse,biol