DAip1, a Dictyostelium homologue of the yeast actin-interacting protein 1,is involved in endocytosis, cytokinesis, and motility

The 64-kD protein DAip1 from Dictyostelium contains nine WD40-repeats and i s homologous to the actin-interacting protein 1,Aip1p, from Saccharomyces c erevisiae, and to related proteins from Caenorhabditis, Physarum, and highe r eukaryotes. We show that DAip1 is localized to dynamic regions of the cel l cortex that are enriched in filamentous actin: phagocytic cups, macropino somes, lamellipodia, and other pseudopodia. In cells expressing green fluor escent protein (GFP)-tagged DAip1, the protein rapidly redistributes into n ewly formed cortical protrusions. Functions of DAip1 in vivo were assessed using null mutants generated by gene replacement, and by overexpressing DAi p1. DAip1-null cells are impaired in growth and their rates of fluid-phase uptake, phagocytosis, and movement are reduced in comparison to wildtype ra tes. Cytokinesis is prolonged in DAip1-null cells and they tend to become m ultinucleate. On the basis of similar results obtained by DAip1 overexpress ion and effects of latrunculin-A treatment, we propose a function for DAip1 in the control of actin depolymerization in vivo, probably through interac tion with cofilin. Our data suggest that DAip1 plays an important regulator y role in the rapid remodeling of the cortical actin meshwork.