Transcriptional activator which regulates the transcription of various genes, including those involved in anti-apoptosis, cell growth, and DNA damage response. Dependent on its binding partner, binds to CRE (cAMP response element) consensus sequences (5'-TGACGTCA-3') or to AP-1 (activator protein 1) consensus sequences (5'-TGACTCA-3'). In the nucleus, contributes to global transcription and the DNA damage response, in addition to specific transcriptional activities that are related to cell development, proliferation and death. In the cytoplasm, interacts with and perturbs HK1- and VDAC1-containing complexes at the mitochondrial outer membrane, thereby impairing mitochondrial membrane potential, inducing mitochondrial leakage and promoting cell death. The phosphorylated form (mediated by ATM) plays a role in the DNA damage response and is involved in the ionizing radiation (IR)-induced S phase checkpoint control and in the recruitment of the MRN complex into the IR-induced foci (IRIF). Exhibits histone acetyltransferase (HAT) activity which specifically acetylates histones H2B and H4 in vitro. In concert with CUL3 and RBX1, promotes the degradation of KAT5 thereby attenuating its ability to acetylate and activate ATM. Can elicit oncogenic or tumor suppressor activities depending on the tissue or cell type (By similarity). Binds DNA as a dimer and can form a homodimer in the absence of DNA. Can form a heterodimer with JUN. Heterodimerization is essential for its transcriptional activity. Interacts with SMAD3 and SMAD4. Binds through its N-terminal region to UTF1 which acts as a coactivator of ATF2 transcriptional activity (By similarity). Interacts with the HK1/VDAC1 complex. Interacts with NBN, MRE11, XPO1, KAT5 and CUL3 (By similarity). Shuttles between the cytoplasm and the nucleus and heterodimerization with JUN is essential for the nuclear localization. Localization to the cytoplasm is observed under conditions of cellular stress and in disease states. Localizes at the mitochondrial outer membrane in response to genotoxic stress. Phosphorylation at Thr-34 is required for its nuclear localization and negatively regulates its mitochondrial localization. Colocalizes with the MRN complex in the IR-induced foci (IRIF) (By similarity). Phosphorylation of Thr-51 by MAPK14 and MAPK11, and at Thr-53 by MAPK1/ERK2, MAPK3/ERK1, MAPK11, MAPK12 and MAPK14 in response to external stimulus like insulin causes increased transcriptional activity. Phosphorylated by PLK3 following hyperosmotic stress. Also phosphorylated and activated by JNK and CaMK4. ATM-mediated phosphorylation at Ser-472 and Ser-480 stimulates its function in DNA damage response. Phosphorylation at Ser-44, Thr-55 and Ser-103 activates its transcriptional activity. Phosphorylation at Thr-51 or Thr-53 enhances acetylation of histones H2B and H4. Belongs to the bZIP family. ATF subfamily. Appears to have histone acetyltransferase (HAT) activity, specifically towards histones H2B and H4 in vitro (By similarity). However, it is not clear if this activity is genuine or caused by contamination with other histone acetyltransferases in the assay.