Changing fos oncoprotein to a jun-independent DNA binding protein with GCN4 dimerization specificity by swapping "leucine zippers".
A structural motif for DNA-binding proteins, the 'leucine zipper', has been proposed for the jun, fos and myc gene products, the yeast transcriptional activator GCN4, and the C/EBP enhancer-binding protein. These proteins all contain a region with four or five leucine residues spaced exactly seven amino acid residues apart whose sequence is consistent with the formation of an amphipathic alpha-helix. It has been proposed that the leucine zipper consists of two interdigitated alpha-helices, one from each monomer, that constitute the dimerization function necessary for high-affinity binding to DNA; an adjacent region of basic residues is thought to be responsible for specific protein-DNA contacts. In support of this model, substitution of the leucine residues within the motif can abolish dimerization and DNA-binding, and a synthetic peptide corresponding to the GCN4 leucine zipper forms alpha-helical dimers. Despite the conserved leucine residues, however, each protein has a distinct dimerization specificity. Specifically, GCN4 homodimer, Jun homodimer and Fos-Jun heterodimer proteins bind to the same DNA site, whereas Fos is unable to form homodimers, bind DNA, or interact with GCN4 (refs 8-14). Here, we alter the dimerization specificity of Fos by precisely replacing its leucine zipper with that from GCN4. This Fos-GCN4 chimaeric protein is able to bind to the target site in the absence of Jun, and can form DNA-binding heterodimers with GCN4 but not with Jun. These results indicate that the leucine zipper is sufficient to confer dimerization specificity and strongly suggest that Fos contacts DNA directly.
Sellers
J W
JW
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Struhl
K
K
D001665:Binding Sites; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000502:physiology* / Q000648:ultrastructure; D005818:Genetic Engineering; D066298:In Vitro Techniques; D007930:Leucine; D046911:Macromolecular Substances; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000502:physiology* / Q000648:ultrastructure; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012045:Regulatory Sequences, Nucleic Acid; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000502:physiology* / Q000648:ultrastructure
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D014157:Transcription Factors; D007930:Leucine