Mutational analyses of Dictyostelium IQGAP-related protein GAPA:: Possible interaction with small GTPases in cytokinesis

GAPA is an IQGAP-related protein and is involved in Dictyostelium cytokinesis. Since mammalian IQGAPs are effectors for Rae/Cdc42, GAPA is also predicted to bind to small GTPases, which are to be identified. In this study, mutant GAPAs were examined for functions in cytokinesis by genetic complementation of gapA(-) cells. Positively charged side chains of Arg(442) and Lys(474) of GAPA, predicted to be present on the surface of interaction with small GTPases, were found to be essential, suggesting, an interaction between GAPA and putative small GTPase in cytokinesis. Also, results from truncated GAPAs indicated that almost the entire region of GAPA homologous to IQGAP is required for cytokinesis in Dictyostelium.