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A more recent version of this article appeared on February 1, 2004
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Submitted on May 26, 2003
Revised on August 9, 2003
Accepted on September 30, 2003
1 Gene Function Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8562, Japan
* Corresponding author. E-mail address: a-nagasaki{at}aist.go.jp.
We have identified a novel gene, dwwA, which is required for cytokinesis of Dictyostelium cells on solid surfaces. Its product, DWWA, contains several motifs, including two WW domains, an IQ motif, a C2 domain and a proline-rich region. On substrates, cells lacking dwwA were multinucleated and larger and flatter than wild-type cells due to their frequent inability to sever the cytoplasmic bridge connecting daughter cells following mitosis. When cultured in suspension, however, dwwA-null cells appeared to carry out cytokinesis normally via a process not driven by the shearing force arising from agitation of the culture. GFP-DWWA localized to the cell cortex and nucleus; analysis of the distributions of various truncation mutants revealed that the N-terminal half of the protein, which contains the C2 domain, is required for the cortical localization of DWWA. The IQ motif of DWWA binds calmodulin in vitro. Given that the scission process is also defective in calmodulin knockdown cells cultured on substrates (Liu et al., 1992), we propose that DWWAs multiple binding domains enable it to function as an adaptor protein, facilitating the scission process through the regulation of Ca2+/calmodulin-mediated remodeling of the actin cytoskeleton and/or modulation of membrane dynamics.
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