During thymocyte development, may play a role in the regulation of apoptosis. Interacts (via IQ domain) with calmodulin/CALM1 only in the absence of Ca(2+) (PubMed:16569770). Interacts with BAX, but not with other Bcl-2 family members, including BAD, BAK1, BCL2, BCL2L1/Bcl-xL and BCL2L11/BimEL (PubMed:16509771). Expressed in thymus (in thymocytes), spleen (in splenocytes), lymph node and lung (PubMed:16509771). Expressed in B-cells and T-cells (at protein level) (PubMed:16569770, PubMed:16509771). Up-regulated during T cell development, including upon the maturation of CD4/CD8 double-positive to CD4 single-positive thymocytes. Phosphorylated at very low levels in resting splenocytes. Rapidly and transiently phosphorylated in response to splenocyte activation. Phosphorylation is increased in cells undergoing apoptosis. No visible phenotype. T-cell development, selection and activation in vivo appear to occur normally in knockout mice. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. AIG1/Toc34/Toc159-like paraseptin GTPase family. IAN subfamily.