Ubiquitylation Dynamics of the Clock Cell Proteome and TIMELESS during a Circadian Cycle

Abstract

Summary: Circadian clocks have evolved as time-measuring molecular devices to help organisms adapt their physiology to daily changes in light and temperature. Transcriptional oscillations account for a large fraction of rhythmic protein abundance. However, cycling of various posttranslational modifications, such as ubiquitylation, also contributes to shape the rhythmic protein landscape. In this study, we used an in vivo ubiquitin labeling assay to investigate the circadian ubiquitylated proteome of Drosophila melanogaster. We find that cyclic ubiquitylation affects MEGATOR (MTOR), a chromatin-associated nucleoporin that, in turn, feeds back to regulate the core molecular oscillator. Furthermore, we show that the ubiquitin ligase subunits CULLIN-3 (CUL-3) and SUPERNUMERARY LIMBS (SLMB) cooperate for ubiquitylating the TIMELESS protein. These findings stress the importance of ubiquitylation pathways in the Drosophila circadian clock and reveal a key component of this system. : Rhythmic deposition of posttranslational modifications such as ubiquitin could underlie circadian rhythms. Here, Szabó et al. explore the cycling ubiquitylation landscape of the proteome in Drosophila and investigate the ubiquitylation of TIMELESS, a core clock protein, by its cognate ubiquitin ligases. Keywords: circadian clock, ubiquitin, proteomics, Drosophila, oscillation, protein degradation, ubiquitin ligase