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Cell. 1997 May 2;89(3):477-86.

Thermally regulated translational control of FRQ mediates aspects of temperature responses in the neurospora circadian clock.

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Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844, USA.


Two forms of FRQ, a central component of the Neurospora circadian clock, arise through alternative in-frame initiation of translation. Either form alone suffices for a functional clock at some temperatures, but both are always necessary for robust rhythmicity. Temperature regulates the ratio of FRQ forms by favoring different initiation codons at different temperatures; when either initiation codon is eliminated, the temperature range permissive for rhythmicity is demonstrably reduced. This temperature-influenced choice of translation-initiation site represents a novel adaptive mechanism that extends the physiological temperature range over which clocks function. Additionally, a temperature-dependent threshold level of FRQ is required to establish the feedback loop comprising the oscillator. These data may explain how temperature limits permissive for rhythmicity are established, thus providing a molecular understanding for a basic characteristic of circadian clocks.

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