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MBC in Press, published online ahead of print July 21, 2004
Mol. Biol. Cell 10.1091/mbc.E04-03-0225

A more recent version of this article appeared on October 1, 2004
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Submitted on March 17, 2004
Accepted on July 9, 2004

TetraThymosin{beta} Is Required for Actin Dynamics in C. elegans and Acts via Functionally Different Actin Binding Repeats

Marleen Van Troys*{dagger}, Kanako Ono{ddagger}, Daisy Dewitte*, Veronique Jonckheere*, Natalie De Ruyck*, Joël Vandekerckhove*, Shoichiro Ono{ddagger}, and Christophe Ampe*

*Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University and Medical Protein Research, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent, Belgium; {ddagger}Department of Pathology, Emory University, Atlanta, GA 30322

Monitoring Editor: David Drubin

Generating specific actin structures via controlled actin polymerization is a prerequisite for eukaryote development and reproduction. We here report on an essential C. elegans protein tetraThymosin{beta} expressed in developing neurons and crucial during oocyte maturation in adults. TetraThymosin{beta} has four repeats each related to the actin monomer sequestering protein thymosin{beta}4 and assists in actin filament elongation. For homologues with similar multirepeat structure a profilin-like mechanism of ushering actin onto filament barbed ends, based on the formation of a 1:1 complex, is proposed to underlie this activity. We, however, demonstrate that tetraThymosin{beta} binds multiple actin monomers via different repeats and in addition also interacts with filamentous actin. All repeats need to be functional for attaining wild-type activity in various in vitro assays. The activities on actin are thus a direct consequence of the repeated structure. In containing both G- and F-actin interaction sites, tetraThymosin{beta} may be reminiscent of nonhomologous multimodular actin regulatory proteins implicated in actin filament dynamics. A mutation that suppresses expression of tetraThymosin{beta} is homozygous lethal. Mutant organisms develop into adults but display a dumpy phenotype and fail to reproduce as their oocytes lack essential actin structures. This strongly suggests that the activity of tetraThymosin{beta} is of crucial importance at specific developmental stages requiring actin polymerization.

{dagger}Corresponding author. E-mail: leen.vantroys{at}ugent.be






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