Functions as a calcium- and DAG-regulated nucleotide exchange factor specifically activating Rap through the exchange of bound GDP for GTP. May also activate other GTPases such as RRAS, RRAS2, NRAS, KRAS but not HRAS. Functions in aggregation of platelets and adhesion of T-lymphocytes and neutrophils probably through inside-out integrin activation. May function in the muscarinic acetylcholine receptor M1/CHRM1 signaling pathway. Forms a signaling complex with RAP1 and BRAF. Interacts with F-actin (By similarity). Interacts with RAP1 (By similarity). Found both in the cytosol and associated with membranes (By similarity). Enriched at juxtamembrane areas and membrane ruffles (By similarity). Localizes to the cell bodies and axons of striatal neurons. Expressed in striatal neurons (at protein level). Expressed in the hematopoietic system. Detected in olfactory structures and deep cortical layers of brain. The N-terminal Ras-GEF domain mediates association with F-actin. Belongs to the RASGRP family.