GIMAP3p is a murine mitochondrial membrane protein belonging to the GTP-binding superfamily and to the immuno-associated nucleotide (IAN) subfamily of nucleotide-binding proteins. The IAN/GIMAP family consists of GTP-binding proteins that share a unique primary structure and whose expression is finely regulated by T-cell receptor signals. Recent studies have shown that IAN/GIMAP family proteins crucially regulate the survival of T cells during development, selection and homeostasis, and are possibly linked to the onset of T-lymphopenia, leukemia and autoimmunity. IAN/GIMAP family proteins might also take part in mitochondrial regulation of lymphocyte apoptosis by interacting with Bcl-2 family proteins. The human GIMAP (GTPase of the immunity-associated protein) gene family includes seven functional members residing on (human) chromosome 7q36.1 and one pseudogene (hGIMAP3).