Human c-Myc is a 439 amino acid transcription factor with a bHLH/LZ (basic Helix-Loop-Helix, Leucine Zipper) domain. c-Myc DNA-binding and transcription function is achieved upon heterodimerization with its partner Max. c-Myc is often overexpressed and mutated in hematopoietic tumors. Mutations frequently result in truncations that remove the transactivation region or in the bHLH/LZ domain required for association with Max and DNA.