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JunB differs from c-Jun in its DNA-binding and dimerization domains, and represses c-Jun by formation of inactive

T Deng1, M Karin

  • 1Department of Pharmacology, University of California, San Diego, School of Medicine, La Jolla 92093-0636.

Genes & Development
|March 1, 1993
PubMed

Insights

JunB protein has reduced gene activation compared to c-Jun due to minor structural changes. Modifying JunB’s DNA-binding and dimerization motifs can restore c-Jun-like activity, highlighting how small sequence variations impact protein function.

Area of Science:

  • Molecular Biology
  • Protein Structure-Function Relationships

Background:

  • JunB and c-Jun are related transcription factors involved in gene regulation.
  • Differences in their functional activities, particularly in activating AP-1-responsive genes and oncogenic transformation, are significant.

Purpose of the Study:

  • To investigate the molecular basis for the functional divergence between JunB and c-Jun.
  • To identify specific amino acid residues responsible for differences in DNA-binding activity and trans-activation capabilities.

Main Methods:

  • Comparative analysis of JunB and c-Jun primary structures, focusing on DNA-binding and dimerization motifs.
  • Site-directed mutagenesis to substitute JunB amino acids with c-Jun sequences.
  • Assays to measure DNA-binding activity, homodimerization, and heterodimerization.

Main Results:

  • Small amino acid differences in the DNA-binding and dimerization motifs of JunB account for a 10-fold decrease in its DNA-binding activity compared to c-Jun.
  • Substitution of four specific amino acids in JunB converted it into a c-Jun-like activator.
  • JunB's leucine zipper, influenced by two glycine residues, mediates attenuation of c-Jun trans-activation by affecting dimerization stability.

Conclusions:

  • Minor alterations in the primary structure of JunB, including conservative changes, lead to significant functional divergence from c-Jun.
  • These findings elucidate how subtle structural modifications can profoundly impact the activity of related transcriptional regulators.

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