Part of a signaling pathway that initiates the aggregation and leads to the formation of aggregation centers or streams. Not essential for cytokinesis, pinocytosis or phagocytosis. Not essential for development, except in starvation-induced aggregation. Binds to small GTPases racE, racC but not rab21. Binds preferentially to GDP-bound racE. Not able to initiate development when placed in starvation buffer. Defect in ability of cells to aggregate in response to starvation. They were unable to form aggregation centers and streams, possibly because of a defect in cAMP relay signaling. Belongs to the RAP1GDS1 family.