Basic leucine zipper (bZIP) domain of Fungal HAC1-like transcription factors: a DNA-binding and dimerization domain
HAC1 (also called Hac1p or HacA) is a bZIP transcription factor that plays a critical role in the unfolded protein response (UPR). The UPR is initiated by the ER-resident protein kinase and endonuclease IRE1, which promotes non-conventional splicing of the HAC1 mRNA, facilitating its translation. HAC1 binds to and activates promoters of genes that encode chaperones and other targets of the UPR. 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.
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