Basic leucine zipper (bZIP) domain of the oncogene Fos (Fos)-like transcription factors: a DNA-binding and dimerization domain
This subfamily is composed of Fos proteins (c-Fos, FosB, Fos-related antigen 1 (Fra-1), and Fra-2), Activating Transcription Factor-3 (ATF-3), and similar proteins. Fos proteins are members of the activator protein-1 (AP-1) complex, which is mainly composed of bZIP dimers of the Jun and Fos families, and to a lesser extent, ATF and musculoaponeurotic fibrosarcoma (Maf) families. The broad combinatorial possibilities for various dimers determine binding specificity, affinity, and the spectrum of regulated genes. The AP-1 complex is implicated in many cell functions including proliferation, apoptosis, survival, migration, tumorigenesis, and morphogenesis, among others. ATF3 is induced by various stress signals such as cytokines, genotoxic agents, or physiological stresses. It is implicated in cancer and host defense against pathogens. It negatively regulates the transcription of pro-inflammatory cytokines and is critical in preventing acute inflammatory syndromes. ATF3 dimerizes with Jun and other ATF proteins; the heterodimers function either as activators or repressors depending on the promoter context. bZIP factors act in networks of homo and heterodimers in the regulation of a diverse set of cellular processes. The bZIP structural motif contains a basic region and a leucine zipper, composed of alpha helices with leucine residues 7 amino acids apart, which stabilize dimerization with a parallel leucine zipper domain. Dimerization of leucine zippers creates a pair of the adjacent basic regions that bind DNA and undergo conformational change. Dimerization occurs in a specific and predictable manner resulting in hundreds of dimers having unique effects on transcription.