A structure, referred to as the 'leucine zipper' [1,2], has been proposed to explain how some eukaryotic gene regulatory proteins work. The leucine zipper consist of a periodic repetition of leucine residues at every seventh position over a distance covering eight helical turns. The segments containing these periodic arrays of leucine residues seem to exist in an α-helical conformation. The leucine side chains extending from one α-helix interact with those from a similar α helix of a second polypeptide, facilitating dimerization; the structure formed by cooperation of these two regions forms a coiled coil [3]. The leucine zipper pattern is present in many gene regulatory proteins, such as:

• The CCATT-box and enhancer binding protein (C/EBP).
• The cAMP response element (CRE) binding proteins (CREB, CRE-BP1, ATFs).
• The Jun/AP1 family of transcription factors.
• The yeast general control protein GCN4.
• The fos oncogene, and the fos-related proteins fra-1 and fos B.
• The C-myc, L-myc and N-myc oncogenes.
• The octamer-binding transcription factor 2 (Oct-2/OTF-2).