Analysis of the Myc and Max interaction specificity with λ repressor-HLH domain fusions

Alessandra Marchetti, Marian Abril-Marti, Barbara Illi, Gianni Cesareni, Sergio Nasi

Research output: Contribution to journalArticlepeer-review


The basic helix-loop-helix domain (bHLH) is present in a large class of transcriptional regulators involved in developmental processes and oncogenesis. It determines DNA binding and specific homo- and heterodimeric protein associations, crucial for protein function. Myc and Max belong to a subset of HLH proteins, containing a leucine zipper (LZ) adjacent to the bHLH domain. They differ in dimerization and functional properties such as DNA binding and transcriptional activation, and their association is required for malignant transformation by Myc. To analyze the interaction specificity of Myc and Max bHLH-LZ domains, we developed a simple Escherichia coli genetic system, which uses the amino-terminal λ phage cI repressor as a reporter for dimerization and allows an easy detection of dimeric interactions. By reciprocal exchanges of different Myc and Max subdomains (helix 1, helix 2 and leucine zipper), we showed that the recognition specificity of Max homodimers as well as of Myc/Max heterodimers is entirely determined by the helix 2-leucine zipper region, the major role being played by the leucine zipper. The Myc LZ was found to prevent homodimeric interactions, thus explaining Myc inability to homodimerize efficiently Moreover, we showed that the system is valid as well for reproducing the interaction of HLH proteins not containing a leucine zipper and that the chimerical proteins maintain sequence-specific DNA binding.

Original languageEnglish
Pages (from-to)541-550
Number of pages10
JournalJournal of Molecular Biology
Issue number3
Publication statusPublished - 1995


  • λ repressor
  • Dimerization specificity
  • HLH domains
  • Myc and Max

ASJC Scopus subject areas

  • Virology
  • Molecular Biology


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