Specific transcription factors belong to a few families

  • The GCN4 basic region-leucine zipper ( b/Zip ) binds DNA as a dimer of two uninterrupted a helices
  • Each monomer of GCN4 domain forms a smoothly curved continuous a helix.
  • The monomers dimerized through zipper region.
  • The basic regions bound to the DNA in the major groove on the opposite side.

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  • GCN4 is a typical member of the b/Zip family of transcription factors.
  • b/Zip family has more than 50 known members from yeast, mammalian and plant cells.
  • GCN4 - 281 amino acids

    •             - DNA-binding region in the C-terminal (~55 AA)
                - basic region (~20 AA) -> 8 charged residues (Arg)
                - zipper region (~35 AA) -> 4-3 repeat of Leu, Val

     
  • Homodimers bind to symetric DNA sequences
  • Heterodimerization alter DNA-binding specificity

  • GCN4 binds to DNA with both specific and nonspecific contacts
  • 4 amino acid side chain form sequence-specific contacts.
  • Asn 235  is at the center of the interaction area

    • - strictly conserved in all b/Zip family members
    - form 2 H-bonds
  • Methyl side chains of Ala 238 and 239 form hydrophobic contacts with methyl group of T3 and T1, respectively.
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