The small G protein RAS2 is involved in the metabolic compensation of the circadian clock in the circadian model Neurospora crassa.

Abstract

Accumulating evidence from both experimental and clinical investigations indicate a tight interaction between metabolism and circadian timekeeping; however, knowledge of the underlying mechanism is still incomplete. Metabolic compensation allows circadian oscillators to run with a constant speed at different substrate levels and therefore is a substantial criterion of a robust rhythm in a changing environment. Because previous data have suggested a central role of RAS2-mediated signaling in the adaptation of yeast to different nutritional environments, we examined the involvement of RAS2 in the metabolic regulation of the clock in the circadian model organism Neurospora crassa. We show that in a ras2-deficient strain, the period is longer than in the control. Moreover, unlike in wild type (wt), in Deltaras2 operation of the circadian clock was affected by glucose: compared with starvation conditions, the period was longer and the oscillation of expression of the frequency (frq) gene was dampened. In constant darkness the delayed phosphorylation of the FRQ protein and the long-lasting accumulation of FRQ in the nucleus were in accordance with the longer period and the less robust rhythm in the mutant. Whereas glucose did not affect the subcellular distribution of FRQ in wt, highly elevated FRQ levels were detected in the nucleus in Deltaras2. RAS2 interacted with the RAS-binding domain of the adenylate cyclase in vitro, and the cAMP analogue 8-Br-cAMP partially rescued the circadian phenotype in vivo. We propose therefore that RAS2 acts via a cAMP-dependent pathway and exerts significant metabolic control on the Neurospora circadian clock.