Basic leucine zipper (bZIP) domain of BTB and CNC homolog (BACH) proteins: a DNA-binding and dimerization domain
BACH proteins are Cap'n'Collar (CNC) Basic leucine zipper (bZIP) transcription factors that are defined by a conserved 43-amino acid region (called the CNC domain) located N-terminal to the bZIP DNA-binding domain. In addition, they contain a BTB domain (Broad complex-Tramtrack-Bric-a-brac domain, also known as the POZ [poxvirus and zinc finger] domain) that is absent in other CNC proteins. Veterbrates contain two members, BACH1 and BACH2. BACH1 forms heterodimers with small Mafs such as MafK to function as a repressor of heme oxygenase-1 (HO-1) gene (Hmox-1) enhancers. It has also been implicated as the master regulator of breast cancer bone metastasis. The BACH1 bZIP transcription factor should not be confused with the protein originally named as BRCA1-Associated C-terminal Helicase1 (BACH1), which has been renamed BRIP1 (BRCA1 Interacting Protein C-terminal Helicase1) and also called FANCJ. BACH2 is a B-cell specific transcription factor that plays a critical role in oxidative stress-mediated apoptosis. It plays an important role in class switching and somatic hypermutation of immunoglobulin genes. 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.