Functions as a Ras GTPase-activating protein. Plays an important role in the expansion and functions of natural killer T (NKT) cells in the liver by negatively regulating RAS activity and the down-stream ERK signaling pathway. Predominantly expressed in hematopoietic tissues. No visible phenotype. The number of natural killer T (NKT) cells in the liver is selectively decreased (around 50%) in mutant mice (PubMed:25652366). It is uncertain whether Met-1 or Met-23 is the initiator.