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:


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