THERMALLY REGULATED TRANSLATIONAL CONTROL OF FRQ MEDIATES ASPECTS OF TEMPERATURE RESPONSES IN THE NEUROSPORA CIRCADIAN CLOCK

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