Editing Alpha helix (section)

=== DNA binding ===
α-Helices have particular significance in [[DNA]] binding motifs, including [[helix-turn-helix]] motifs, [[leucine zipper]] motifs and [[zinc finger]] motifs. This is because of the convenient structural fact that the diameter of an α-helix is about {{cvt|12|Å|nm}} including an average set of sidechains, about the same as the width of the major groove in B-form [[DNA]], and also because [[coiled-coil]] (or leucine zipper) dimers of helices can readily position a pair of interaction surfaces to contact the sort of symmetrical repeat common in double-helical DNA.<ref>Branden & Tooze, chapter 10</ref>  An example of both aspects is the [[transcription factor]] Max (see image at left), which uses a helical coiled coil to dimerize, positioning another pair of helices for interaction in two successive turns of the DNA major groove.