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Protein Motifs: the Helix-Turn-Helix Motif

  1. Brian W Matthews

Published Online: 28 SEP 2007

DOI: 10.1002/9780470015902.a0002712



How to Cite

Matthews, B. W. 2007. Protein Motifs: the Helix-Turn-Helix Motif. eLS. .

Author Information

  1. Howard Hughes Medical Institute and University of Oregon, Oregon, USA

Publication History

  1. Published Online: 28 SEP 2007


The helix-turn-helix motif was first observed in the structures of certain proteins that bind to specific regulatory sites on deoxyribonucleic acid (DNA). It is made up of a part of the protein comprising an α-helix followed by a turn followed by a second α-helix aligned approximately 120° to the first. When the protein binds to its regulatory site, the second α-helix of the helix-turn-helix occupies one of the grooves on the DNA and is critical in recognizing the correct target.


  • Cro;
  • CAP;
  • DNA binding;
  • gene regulation