a basic helix-loop-helix leucine-zipper protein that, as a homodimer, binds promoter regions of melanocyte-specific genes (e.g. tyrosinase). Mouse and human proteins (both ≈415 amino acids) share 95% sequence homology. At least a dozen mutations cause a type of Waardenburg syndrome that includes white forelock, heterochromia iridis, and congenital hearing loss. The protein is named after the microphthalmia-associated transcription factor of mouse.