Helix-Turn-Helix Motifs

**Definition:** The first DNA-binding protein motif to be recognized. Helix-turn-helix motifs were originally identified in bacterial proteins but have since been found in hundreds of DNA-BINDING PROTEINS from both eukaryotes and prokaryotes. They are constructed from two alpha helices connected by a short extended chain of amino acids, which constitute the turn. The two helices are held at a fixed angle, primarily through interactions between the two helices. (From Alberts et al., Molecular Biology of the Cell, 3d ed, p408-9)

**Tree numbers:** - G02.111.570.820.709.275.500.360.360

**Synonyms:** - HTH Motifs - Motifs, Helix-Turn-Helix