Functions as a calcium- and diacylglycerol (DAG)-regulated nucleotide exchange factor specifically activating Ras through the exchange of bound GDP for GTP (PubMed:9789079, PubMed:9582122). Activates the Erk/MAP kinase cascade. Regulates T-cell/B-cell development, homeostasis and differentiation by coupling T-lymphocyte/B-lymphocyte antigen receptors to Ras. Regulates NK cell cytotoxicity and ITAM-dependent cytokine production by activation of Ras-mediated ERK and JNK pathways (By similarity). Functions in mast cell degranulation and cytokine secretion, regulating FcERI-evoked allergic responses. May also function in differentiation of other cell types. Proto-oncogene, which promotes T-cell lymphomagenesis when its expression is deregulated (By similarity). Autoinhibited (By similarity). Activated by diacylglycerol and calcium binding, which induces a conformational change releasing the autoinhibitory state (PubMed:9582122). Regulated by DGKA. Regulated by DGKZ. Regulated by PLC gamma and F-actin polymerization (By similarity). Homodimer. Forms a signaling complex with DGKZ and HRAS. Interacts with F-actin. Interacts with SKAP1 (By similarity). Found both in the cytosol and associated with membranes. Relocalization to the cell membrane upon activation is F-actin-dependent (By similarity). Translocates to the Golgi in response to phorbol ester or nerve growth factor (By similarity). Localizes to somata and dendrites but not to axons of hippocampal pyramidal cells. Specifically expressed in brain with higher density in hippocampal CA1 and CA3 fields. Detected in interneurons and projection neurons with no restriction to any neuronal type or neurotransmitter phenotype but not detected in glial cells. Expressed in the hematopoietic system. Expressed in several neuronal types of the hippocampus and entorhinal cortex (at protein level). Expression appears in neurons of the hippocampus during the first 2 weeks after birth (at protein level). The phorbol-ester/DAG-type zinc finger is the principal mediator of the targeting to membranes and is required for functional activation through DAG-binding. Two EF-hand domains are present. However, only EF-hand 1 (and not EF-hand 2) binds calcium. Belongs to the RASGRP family.