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Integrity of FOS B leucine zipper is essential for its interaction with JUN proteins

R P Ryseck1, K Kovary, R Bravo

  • 1Squibb Institute for Medical Research, Department of Molecular Biology, Princeton, New Jersey 08543-4000.

Oncogene
|July 1, 1990
PubMed

Insights

Fos B protein interacts with JUN proteins, crucial for gene regulation. Altering its leucine zipper structure, essential for this interaction, prevents binding and impacts cellular responses.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Biochemistry

Background:

  • Fos B is a nuclear protein homologous to c-fos.
  • Its expression is induced during the G0/G1 cell cycle transition.
  • FOS B protein forms complexes with JUN proteins (c-JUN, JUN B, JUN D).

Purpose of the Study:

  • To investigate the role of the 'leucine zipper' in FOS B protein interactions.
  • To determine how mutations in the FOS B leucine zipper affect binding to JUN proteins and AP-1 DNA sequences.

Main Methods:

  • Immunoprecipitation studies were used to analyze protein complex formation.
  • Site-directed mutagenesis was employed to alter leucine residues within the FOS B 'leucine zipper'.
  • Assays were performed to assess protein-protein interactions and DNA binding affinity.

Main Results:

  • Mutations of leucine residues 1, 3, or 5 to proline in the FOS B leucine zipper significantly inhibited association with JUN proteins.
  • Substitution of a conserved leucine with isoleucine resulted in a 50% inhibition of FOS B-JUN interaction.
  • Major alterations to the alpha-helical structure of the leucine zipper abolished FOS B interaction with all tested JUN proteins.

Conclusions:

  • The 'leucine zipper' domain is critical for FOS B protein interaction with JUN proteins.
  • The alpha-helical structure of the leucine zipper is essential for mediating these protein-protein interactions.
  • These findings elucidate the structural requirements for FOS B/JUN complex formation and AP-1 transcriptional activity.

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