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A more recent version of this article appeared on November 1, 2006
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Submitted on April 7, 2006
Revised on July 5, 2006
Accepted on August 8, 2006
Institut de Biochimie et Génétique Cellulaires, Centre National de la Recherche Scientifique UMR 5095, Université Victor Segalen/Bordeaux II, F-33077 Bordeaux Cedex, France
Monitoring Editor: Fred Chang
Most eukaryotic cells spend most of their life in a quiescent state, poised to respond to specific signals to proliferate. In the case of S. cerevisiae, entry into and exit from quiescence are dependent only on the availability of nutrients in the environment. The transition from quiescence to proliferation requires not only drastic metabolic changes but also a complete remodeling of various cellular structures. Here, we describe an actin cytoskeleton organization specific of the yeast quiescent state. When cells cease to divide, actin is reorganized into structures that we named "actin bodies". We show that actin bodies contain F-actin and several actin binding proteins such as fimbrin and capping protein. Further, by contrast to actin patches or cables, actin bodies are mostly immobile and we could not detect any actin filament turnover. Finally, we show that upon cells refeeding, actin bodies rapidly disappear and actin cables and patches can be assembled in the absence of de novo protein synthesis. This led us to propose that actin bodies are a reserve of actin that can be immediately mobilized for actin cables and patches formation upon reentry into a proliferation cycle.
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