Leucine zipper protein This is the leucine zipper segment from GCN4, the yeast transcription factor. It is a 2-stranded, parallel coiled-coil. The leucines are colored red. Notice that they are side-by-side. One interaction uses 3 leucines. O'Shea, E. K., Klemm, J. D., Kim, P. S., Alber, T.: X-ray structure of the GCN4 leucine zipper, a two-stranded, parallel coiled coil. Science 254 pp. 539 (1991) (PubMed) 2zta (PDB)