GTPase activator for the nuclear Ras-related regulatory protein RAP-1A (KREV-1), converting it to the putatively inactive GDP-bound state. Homodimer and heterodimer with RAP1B. Significant expression seen in the brain, kidney and pancreas. Abundant in the cerebral cortex and expressed at much lower levels in the spinal cord. Not detected in the lymphoid tissues. By 12-O-tetradecanoylphorbol-13-acetate (TPA) in promyelocytic HL-60 cells. Truncated N-terminus. Extended N-terminus.