X-Message-Number: 12400 Date: Sat, 11 Sep 1999 17:31:10 -0400 From: Jan Coetzee <> Subject: Light Response of the Timeless I wonder if the larvae (whose time protein was inhibited) lived longer. A Role for the Proteasome in the Light Response of the Timeless Clock Protein Nirinjini Naidoo, Wei Song, Melissa Hunter-Ensor, * Amita Sehgal 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. Howard Hughes Medical Institute, Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. * Present address: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. To whom correspondence should be addressed. E-mail: Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=12400