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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Acetylcysteine / analogs & derivatives
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Acetylcysteine / pharmacology
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Animals
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Biological Clocks*
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Cells, Cultured
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Circadian Rhythm*
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Cysteine Endopeptidases / physiology*
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Cysteine Proteinase Inhibitors / pharmacology
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Darkness
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Drosophila
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Drosophila Proteins*
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Feedback
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Insect Proteins / metabolism*
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Leucine / analogs & derivatives
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Leucine / pharmacology
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Leupeptins / pharmacology
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Light*
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Multienzyme Complexes / physiology*
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Neurons / metabolism*
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Phosphorylation
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Phosphotyrosine / metabolism
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Protease Inhibitors / pharmacology
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Proteasome Endopeptidase Complex
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Ubiquitins / metabolism
Substances
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Cysteine Proteinase Inhibitors
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Drosophila Proteins
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Insect Proteins
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Leupeptins
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Multienzyme Complexes
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Protease Inhibitors
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Ubiquitins
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carbobenzoxy-leucyl-leucyl-norvalinal
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tim protein, Drosophila
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lactacystin
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Phosphotyrosine
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex
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Leucine
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ubenimex
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leupeptin
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Acetylcysteine