This family consists of the leucine zipper dimerization domain found in both cellular c-Myc proto-oncogenes and viral v-Myc oncogenes. dimerization via the leucine zipper motif with other basic helix-loop-helix-leucine zipper (b/HLH/lz) proteins such as Max is required for efficient DNA binding. The Myc-Max dimer is a transactivating complex activating expression of growth related genes promoting cell proliferation. The dimerization is facilitated via interdigitating leucine residues every 7th position of the alpha helix. Like charge repulsion of adjacent residues in this region perturbs the formation of homodimers with heterodimers being promoted by opposing charge attractions.