A Role for the Proteasome in the Light Response of the Timeless Clock Protein

Abstract

The cyclic expression of the period (PER) and timeless (TIM) proteins is critical for the molecular circadian feedback loop in Drosophila. The entrainment by light of the circadian clock is mediated by a reduction in TIM levels. To elucidate the mechanism of this process, the sensitivity of TIM regulation by light was tested in an in vitro assay with inhibitors of candidate proteolytic pathways. The data suggested that TIM is degraded through a ubiquitin-proteasome mechanism. In addition, in cultures from third-instar larvae, TIM degradation was blocked specifically by inhibitors of proteasome activity. Degradation appeared to be preceded by tyrosine phosphorylation. Finally, TIM was ubiquitinated in response to light in cultured cells.

Circadian phase-specific degradation of the F-box protein ZTL is mediated by the proteasome

“…In Drosophila, both timeless and period levels are degraded via a proteasome-dependent pathway (37,38). Similarly, in Neurospora, FRQ protein phosphorylation status determines the FRQ protein degradation rate.…”

Molecular Analysis of Sleep: Wake Cycles inDrosophila

“…2) (Naidoo et al 1999;Lin et al 2001), but until recently, other molecular components of this response were not known. We recently identified one such component through the analysis of a mutation found in one of our fly stocks (Koh et al 2006a).…”

A PER/TIM/DBT Interval Timer forDrosophila's Circadian Clock

“…Subsequently, this cell line (S2; Schneider's line 2), has become an important tool for investigating the function of Drosophila's circadian clock using transcription assays (Darlington et al 1998), immunoprecipitation assays (Ceriani et al 1999), degradation assays (Naidoo et al 1999), and assays of phophorylation and dephosphorylation (cf. Ko et al 2002;Sathyanarayanan et al 2004).…”