GTPase-activating protein (GAP) that stimulates the intrinsic GTPase activity of Ras proteins, such as NRAS, facilitating their transition from the active GTP-bound state to the inactive GDP-bound state, thereby terminating Ras signaling. {ECO:0000269|PubMed:11389730, ECO:0000269|PubMed:2123878, ECO:0000269|PubMed:3201259, ECO:0000269|PubMed:8360177}. This is the function of Ensembl gene identifier ENSG00000145715 (RASA1, RAS p21 protein activator 1).