Leucine Zipper with DNA (1YSA) - Leucine Zippers are a class of proteins that bind to DNA at specific sites within the promoters of genes. When the protein is bound to the promoter, transcription is stimulated and the gene is "expressed". This class of DNA binding proteins gets its name from the regular pattern of leucine residues within the two alpha helices (pictured below on the right). Being hydrophobic, the leucines cause two adjacent alpha helices to be "zippered" together by hydrophobic interactions. On the end of each alpha helix is the DNA binding region which contains basic amino acids that form ionic bonds with the acidic DNA. These regions also fit within the major groove of the DNA allowing for contact between the amino acid side chains of the protein and the nitrogenous bases of the DNA. This contact makes it possible for the zipper to bind to a specific sequence of DNA.
Many different leucine zipper genes can be found in the genome of a given organism, each with a specific set of target genes it turns on. In addition to leucine zippers, there are other classes of DNA binding proteins with similar functions but different structures and different target genes. Together, these different DNA binding proteins help to control gene expression so that complex organisms develop and function correctly. Mutations in some DNA binding proteins can lead to cancerous cell growth as a result of inappropriate gene expression.
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