Serine/threonine protein kinase which activates checkpoint signaling upon double strand breaks (DSBs), apoptosis and genotoxic stresses such as ionizing ultraviolet A light (UVA), thereby acting as a DNA damage sensor. Recognizes the substrate consensus sequence [ST]-Q. Phosphorylates 'Ser-139' of histone variant H2AX at double strand breaks (DSBs), thereby regulating DNA damage response mechanism. Also plays a role in pre-B cell allelic exclusion, a process leading to expression of a single immunoglobulin heavy chain allele to enforce clonality and monospecific recognition by the B-cell antigen receptor (BCR) expressed on individual B-lymphocytes. After the introduction of DNA breaks by the RAG complex on one immunoglobulin allele, acts by mediating a repositioning of the second allele to pericentromeric heterochromatin, preventing accessibility to the RAG complex and recombination of the second allele. Also involved in signal transduction and cell cycle control. May function as a tumor suppressor. Necessary for activation of ABL1 and SAPK. Phosphorylates DYRK2, CHEK2, p53/TP53, FBXW7, FANCD2, NFKBIA, BRCA1, CTIP, nibrin (NBN), TERF1, UFL1, RAD9, UBQLN4 and DCLRE1C (PubMed:9843217, PubMed:9733515, PubMed:10550055, PubMed:10766245, PubMed:10839545, PubMed:10910365, PubMed:10802669, PubMed:10973490, PubMed:11375976, PubMed:12086603, PubMed:15456891, PubMed:19965871, PubMed:30612738, PubMed:30886146, PubMed:26774286). May play a role in vesicle and/or protein transport. Could play a role in T-cell development, gonad and neurological function. Plays a role in replication-dependent histone mRNA degradation. Binds DNA ends. Phosphorylation of DYRK2 in nucleus in response to genotoxic stress prevents its MDM2-mediated ubiquitination and subsequent proteasome degradation. Phosphorylates ATF2 which stimulates its function in DNA damage response. Phosphorylates ERCC6 which is essential for its chromatin remodeling activity at DNA double-strand breaks (PubMed:29203878). Phosphorylates TTC5/STRAP at 'Ser-203' in the cytoplasm in response to DNA damage, which promotes TTC5/STRAP nuclear localization (PubMed:15448695). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Inhibited by wortmannin. Homodimer (PubMed:28508083). Dimers or tetramers in inactive state. On DNA damage, autophosphorylation dissociates ATM into monomers rendering them catalytically active. Binds p53/TP53, ABL1, BRCA1, NBN/nibrin and TERF1. Part of the BRCA1-associated genome surveillance complex (BASC), which contains BRCA1, MSH2, MSH6, MLH1, ATM, BLM, PMS2 and the RAD50-MRE11-NBN protein complex. This association could be a dynamic process changing throughout the cell cycle and within subnuclear domains. Interacts with RAD17; DNA damage promotes the association. Interacts with EEF1E1; the interaction, induced on DNA damage, up-regulates TP53. Interacts with DCLRE1C, KAT8, KAT5, NABP2, ATMIN and CEP164. Interacts with AP2B1 and AP3B2; the interaction occurs in cytoplasmic vesicles (By similarity). Interacts with TELO2 and TTI1. Interacts with DDX1. Interacts with BRAT1. Interacts with CYREN (via XLF motif) (By similarity). Primarily nuclear. Found also in endocytic vesicles in association with beta-adaptin. Found in pancreas, kidney, skeletal muscle, liver, lung, placenta, brain, heart, spleen, thymus, testis, ovary, small intestine, colon and leukocytes. By ionizing radiation. The FATC domain is required for interaction with KAT5. Phosphorylated by NUAK1/ARK5 (PubMed:12409306). Autophosphorylation on Ser-367, Ser-1893, Ser-1981 correlates with DNA damage-mediated activation of the kinase (PubMed:12556884, PubMed:16141325, PubMed:16858402, PubMed:21144835, PubMed:27664052). During the late stages of DNA damage response, dephosphorylated following deacetylation by SIRT7, leading to ATM deactivation (PubMed:30944854). Acetylation, on DNA damage, is required for activation of the kinase activity, dimer-monomer transition, and subsequent autophosphorylation on Ser-1981 (PubMed:12556884, PubMed:16141325, PubMed:16858402, PubMed:17923702, PubMed:21144835). Acetylated in vitro by KAT5/TIP60 (PubMed:16141325). Deacetylated by SIRT7 during the late stages of DNA damage response, promoting ATM dephosphorylation and subsequent deactivation (PubMed:30944854). The disease is caused by variants affecting the gene represented in this entry. Defects in ATM may contribute to T-cell acute lymphoblastic leukemia (TALL) and T-prolymphocytic leukemia (TPLL). TPLL is characterized by a high white blood cell count, with a predominance of prolymphocytes, marked splenomegaly, lymphadenopathy, skin lesions and serous effusion. The clinical course is highly aggressive, with poor response to chemotherapy and short survival time. TPLL occurs both in adults as a sporadic disease and in younger AT patients. Defects in ATM may contribute to B-cell non-Hodgkin lymphomas (BNHL), including mantle cell lymphoma (MCL). Defects in ATM may contribute to B-cell chronic lymphocytic leukemia (BCLL). BCLL is the commonest form of leukemia in the elderly. It is characterized by the accumulation of mature CD5+ B-lymphocytes, lymphadenopathy, immunodeficiency and bone marrow failure. Belongs to the PI3/PI4-kinase family. ATM subfamily. Truncated N-terminus. Probable cloning artifact. Truncated N-terminus. Probable cloning artifact. Ataxia telangiectasia mutated entry