Heterodimerizes with proteins of the JUN family to form an AP-1 transcription factor complex, thereby enhancing their DNA binding activity to gene promoters containing an AP-1 consensus sequence 5'-TGA[GC]TCA-3' and enhancing their transcriptional activity (PubMed:2498083, PubMed:1900040). As part of the AP-1 complex, facilitates enhancer selection together with cell-type-specific transcription factors by collaboratively binding to nucleosomal enhancers and recruiting the SWI/SNF (BAF) chromatin remodeling complex to establish accessible chromatin (PubMed:29272704). Together with JUN, plays a role in activation-induced cell death of T cells by binding to the AP-1 promoter site of FASLG/CD95L, and inducing its transcription in response to activation of the TCR/CD3 signaling pathway (By similarity). Exhibits transactivation activity in vitro (PubMed:17241283). Involved in the display of nurturing behavior towards newborns (PubMed:8706134). May play a role in neurogenesis in the hippocampus and in learning and memory-related tasks by regulating the expression of various genes involved in neurogenesis, depression and epilepsy (PubMed:23303048, PubMed:30902680). Implicated in behavioral responses related to morphine reward and spatial memory (PubMed:9294222, PubMed:18407360). Exhibits lower transactivation activity than isoform 1 in vitro (PubMed:17241283). The heterodimer with JUN does not display any transcriptional activity, and may thereby act as an transcriptional inhibitor (PubMed:1900040). May be involved in the regulation of neurogenesis in the hippocampus (PubMed:23303048). May play a role in synaptic modifications in nucleus accumbens medium spiny neurons and thereby play a role in adaptive and pathological reward-dependent learning, including maladaptive responses involved in drug addiction (PubMed:23319622). Seems to be more stably expressed with a half-life of ~9.5 hours in cell culture as compared to 1.5 hours half-life of isoform 1 (PubMed:18407360). Heterodimer; binds to DNA as heterodimer (PubMed:2498083, PubMed:1900040). Component of an AP-1 transcription factor complex; composed of FOS-JUN heterodimers (PubMed:2498083, PubMed:1900040). As part of the AP-1 transcription factor complex, forms heterodimers with JUN, JUNB or JUND, thereby binding to the AP-1 consensus sequence and stimulating transcription (PubMed:2498083, PubMed:1900040). Interacts with the BAF multiprotein chromatin-remodeling complex subunits SMARCB1 and SMARCD1 (PubMed:29272704). Interacts with ARID1A and JUN (PubMed:29272704). Homodimer under oxidizing conditions and monomer under reducing conditions (in vitro) (By similarity). Heterodimer; binds to DNA as heterodimer (PubMed:1900040). Forms heterodimers with JUNB, JUN or JUND; thereby binding to the AP-1 consensus sequence but does not stimulate transcription (PubMed:1900040). Forms heterodimers with JUND under oxidizing conditions (By similarity). Expressed in brain, including the preoptic area of the hypothalamus, the main and accessory olfactory bulbs, the pyriform cortex and the hippocampus (at protein level) (PubMed:8706134, PubMed:23303048). Expressed in the neurons of the subgranular zone of the dentate gyrus in the hippocampus (at protein level) (PubMed:23303048, PubMed:30902680). Expressed in pyramidal cells in CA1 and CA3, in the dentate gyrus and the nucleus accumbens of the striatum (at protein level) (PubMed:9294222, PubMed:26446228). Expressed in the core and shell of the nucleus accumbens of the striatum (at protein level) (PubMed:20473292). Expressed in the neurons of the subgranular zone of the dentate gyrus in the hippocampus (at protein level) (PubMed:23303048). Induced by growth factors (PubMed:2498083). Up-regulated in the preoptic area of the hypothalamus after 6 hours of exposure to pups (PubMed:8706134). Induced by cocaine in the striatum (PubMed:9294222). Induced by kainic acid (PubMed:23303048). Induced in the hippocampus by novelty exposure and spatial learning (PubMed:26446228). Induced by cocaine in the striatum. Induced by cocaine in the striatum (PubMed:9294222). Induced by chronic social defeat stress, with resilient mice showing the greatest induction in both core and shell nucleus accumbens subregions (PubMed:20473292). Binds DNA via bZIP domain; DNA-binding is under control of cellular redox homeostasis (in vitro) (By similarity). To enable DNA binding, the bZIP domain must undergo a conformational rearrangement which requires the reduction of the interchain disulfide bond between FosB and JunD (in vitro) (By similarity). The bZIP domain is able to form homomeric oligomers via formation of interchain disulfide bonds under non-reducing conditions (in vitro) (By similarity). Under reducing conditions, the disulfide-bonded homomeric species dissociates into monomers (in vitro) (By similarity). Phosphorylated. Phosphorylated at Ser-27 by CSNK2A1; phosphorylation increases protein stability and transactivation potential. Deficiency in the ability to nurture young animals and the majority of pups die within 1-2 days of birth (PubMed:8706134). Impaired nurturing behavior towards newborns is observed in postpartum mothers as well as in young females and males (PubMed:8706134). Failure in AP-1 binding activity after repeated cocaine administration (PubMed:9294222). Exaggerated locomotor activation in response to initial cocaine exposures as well as robust conditioned place preference to a lower dose of cocaine, but lack of increment in cocaine-induced hyperactivity over 6 days (i.e. sensitization) (PubMed:9294222). Decreased sensitivity to rewarding properties of morphine and spatial memory impairment (PubMed:18407360). Decreased proliferation and increased ectopic migration of neural progenitor cells in the hippocampus (PubMed:23303048). Exhibit impaired adult hippocampal neurogenesis and spontaneous epilepsy with depressive behavior (PubMed:23303048). Altered gene expression in the hippocampus, including genes implicated in neurogenesis, depression, or epilepsy (PubMed:23303048). Knockout in hippocampal neurons, including neurons of the subgranular zone of the dentate gyrus, leads to a reduction of antidepressant-induced neurogenesis and impedes hippocampus-dependent learning in the novel object recognition task (PubMed:30902680). Belongs to the bZIP family. Fos subfamily.