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J. Cell Biol.,
Volume 142, Number 3, August 10, 1998 723-733
Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202
Here we describe the identification of a
novel 37-kD actin monomer binding protein in budding
yeast. This protein, which we named twinfilin, is composed of two cofilin-like regions. In our sequence database searches we also identified human, mouse, and Caenorhabditis elegans homologues of yeast twinfilin,
suggesting that twinfilins form an evolutionarily conserved family of actin-binding proteins. Purified recombinant twinfilin prevents actin filament assembly by
forming a 1:1 complex with actin monomers, and inhibits the nucleotide exchange reaction of actin monomers.
Despite the sequence homology with the actin filament
depolymerizing cofilin/actin-depolymerizing factor
(ADF) proteins, our data suggests that twinfilin does
not induce actin filament depolymerization. In yeast
cells, a green fluorescent protein (GFP)-twinfilin fusion protein localizes primarily to cytoplasm, but also to
cortical actin patches. Overexpression of the twinfilin
gene (TWF1) results in depolarization of the cortical
actin patches. A twf1 null mutation appears to result in
increased assembly of cortical actin structures and is
synthetically lethal with the yeast cofilin mutant cof1-22, shown previously to cause pronounced reduction in
turnover of cortical actin filaments. Taken together,
these results demonstrate that twinfilin is a novel,
highly conserved actin monomer-sequestering protein
involved in regulation of the cortical actin cytoskeleton.
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