Heterodimerizes with proteins of the JUN family to form an AP-1 transcription factor complex, thereby enhancing their DNA binding activity to an AP-1 consensus sequence 5'-TGA[GC]TCA-3' and enhancing their transcriptional activity (By similarity). Exhibits transactivation activity in vitro (By similarity). 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 (By similarity). 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). Involved in the display of nurturing behavior towards newborns (By similarity). 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 (By similarity). Implicated in behavioral responses related to morphine reward and spatial memory (By similarity). Heterodimer; binds to DNA as heterodimer (By similarity). Component of an AP-1 transcription factor complex; composed of FOS-JUN heterodimers (By similarity). 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 (By similarity). Interacts with the BAF multiprotein chromatin-remodeling complex subunits SMARCB1 and SMARCD1 (By similarity). Interacts with ARID1A and JUN (By similarity). 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. Belongs to the bZIP family. Fos subfamily.