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Basic leucine zipper (bZIP) domain of Hepatic leukemia factor (HLF) and similar proteins: a DNA-binding and dimerization domain HLF, also called vitellogenin gene-binding protein (VBP) in birds, is a circadian clock-controlled Basic leucine zipper (bZIP) transcription factor which is a direct transcriptional target of CLOCK/BMAL1. It is implicated, together with bZIPs DBP and TEF, in the regulation of genes involved in the metabolism of endobiotic and xenobiotic agents. Triple knockout mice display signs of early aging and suffer premature death, likely due to impaired defense against xenobiotic stress. A leukemogenic translocation results in the chimeric fusion protein E2A-HLF that results in a rare form of pro-B-cell acute lymphoblastic leukemia (ALL). 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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