DICTYOSTELIUM RASG IS REQUIRED FOR NORMAL MOTILITY AND CYTOKINESIS, BUT NOT GROWTH

RasG is the most abundant Ras protein in growing Dictyostelium cells a nd the closest relative of mammalian Ras proteins. We have generated n ull mutants in which expression of RasG is completely abolished. Unexp ectedly, RasG(-) cells are able to grow at nearly wild-type rates, How ever, they exhibit defective cell movement and a wide range of defects in the control of the actin cytoskeleton, including a loss of cell po larity, absence of normal lamellipodia, formation of unusual small, pu nctate polymerized actin structures, and a large number of abnormally long filopodia. Despite their lack of polarity and abnormal cytoskelet on, mutant cells perform normal chemotaxis. However, rasG(-) cells are unable to perform normal cytokinesis, becoming multinucleate when gro wn in suspension culture. Taken together, these data suggest a princip al role for RasG in coordination of cell movement and control of the c ytoskeleton.