During thymocyte development, may play a role in the regulation of apoptosis (By similarity). GTPase which exhibits a higher affinity for GDP than for GTP. May interact (via IQ domain) with calmodulin/CALM1 only in the absence of Ca(2+) (By similarity). Interacts with BAX, but not with other Bcl-2 family members (By similarity). Highly expressed in spleen and peripheral blood leukocytes that contain mostly T- and B-lymphocytes. Expressed specifically in resting T- and B-lymphocytes and expression significantly decreases during B- or T-lymphocyte activation. Expressed at lower levels in thymus, ovary, colon and small intestine. Phosphorylated at very low levels in resting splenocytes. Rapidly and transiently phosphorylated in response to splenocyte activation. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. AIG1/Toc34/Toc159-like paraseptin GTPase family. IAN subfamily.