Zinc finger, helix-turn-helix, and leucine zipper motifs in the same regulatory protein. The Gal4 protein (Gal4p), a yeast transcription activator, is a dimer, held together by a leucine zipper. Each of the two DNA-binding domains contains two Zn²⁺ ions, which help hold the recognition helix (red) of the helix-turn-helix motif in the proper geometry for DNA recognition.