Plays a role in T lymphocyte development and the optimal generation of CD4/CD8 double-positive thymocytes (By similarity). Inhibitor of GSK3A, possibly by sequestering GSK3A in cytoplasmic vesicles and impairing its translocation to the nucleus. Consequently, impairs GSK3A-dependent transcriptional program and regulation of the DNA damage response occurring during T cells proliferation (PubMed:29382851). Required for the survival of peripheral T cells, natural killer (NK) and NK T-cell development and the maintenance of normal liver function (By similarity). May promote the survival of mature T lymphocytes upon cytokine withdrawal (By similarity). May regulate Ca(2+) homeostasis by modulating lysosomal Ca(2+) stores, preventing its accumulation in the absence of T cell activation (By similarity). May play a role in mitochondrial DNA segregation in hematopoietic tissues (By similarity). Is a regulator of liver endothelial cell homeostasis (By similarity). Interacts with BAD, BAK1, BAX, BCL2, BCL2L1/Bcl-xL and BCL2L11/BimEL (PubMed:16509771). The interaction with BAX is increased, when cells initiate apoptosis upon IL2 withdrawal (PubMed:16509771). Also interacts with BCL2 (By similarity). Forms a complex with BCL2L1 or MCL1 and HSPA8/HSC70; the interaction between HSPA8 and BCL2L1 or MCL1 is impaired in the absence of GIMAP5 (By similarity). May interact (via N-terminus) with microtubules (By similarity). The mitochondrial localization originally reported was observed with C-terminally tagged protein and was not confirmed in later publications. Widely expressed with high levels in lymph node and spleen (PubMed:14724691). High expression found in T lymphocytes, including CD4 and CD8-positive T-cells, and monocytes (PubMed:14724691, PubMed:29382851). Very low expression levels in B-lymphocytes (PubMed:14724691). The disease may be caused by variants affecting the gene represented in this entry. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. AIG1/Toc34/Toc159-like paraseptin GTPase family. IAN subfamily.