<prompt> In leucine zipper model, Leucine residue is seen after every3 amino acids6 amino acids7 amino acids12 amino acids  <response>: An a helix in which there is a periodic repeat of leucine residues at every seventh position. This occurs for eight helical turns and four leucine repeats. Similar structures have been found in a number of other proteins associated with the regulation of transcription in mammalian and yeast cells. It is thought that this structure allows two identical monomers or heterodimers eg, Fos-Jun or Jun-Jun to zip together in a coiled-coil and form a tight dimeric complex This protein-protein interaction may serve to enhance the association of the separate DNA binding domains with their target 