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* Medical Research Council Laboratory for Molecular Cell Biology, RasG is the most abundant Ras protein in
growing Dictyostelium cells and the closest relative of
mammalian Ras proteins. We have generated null mutants in which expression of RasG is completely abolished. Unexpectedly, RasG
Department of Physiology, and § Department of Molecular
Medicine, University College London, London WC1E 6BT, United Kingdom; and
Department of Microbiology and
Immunology and Department of Medical Genetics, University of British Columbia, Vancouver V6T 1Z3, Canada
cells are able to grow at
nearly wild-type rates. However, they exhibit defective
cell movement and a wide range of defects in the control of the actin cytoskeleton, including a loss of cell polarity, absence of normal lamellipodia, formation of unusual small, punctate polymerized actin structures, and
a large number of abnormally long filopodia. Despite
their lack of polarity and abnormal cytoskeleton, mutant cells perform normal chemotaxis. However, rasG
cells are unable to perform normal cytokinesis, becoming multinucleate when grown in suspension culture.
Taken together, these data suggest a principal role for
RasG in coordination of cell movement and control of
the cytoskeleton.
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