MITF (Microphthalmia-associated transcription factor) is a member of the MiT/TFE family of molecules. Although it has a predicted MW of 58 kDa, it runs anomalously in SDS-PAGE at 57-66 kDa. MITF-A1 is found in melanocytes and RPEs where it regulates melanin synthesis via tyrosinase and TRP-1 gene expression. Human MITF-A1 is 526 amino acids (aa) in length. It contains a bHLH DNA binding region (aa 309-369) and a Leu-zipper domain (aa 374-395). There are three phosphorylation sites at Ser54/405/414, and two SUMOylation sites at Arg289/423. MITF-A1 acts as either a homodimer, or heterodimer with TFE3, TFEB or TFEC. Multiple splice variants exist, with each variant expressing one of two isoforms that are defined by the presence (#1), or absence (#2), of aa 294-299. One variant has a deletion of aa 139-194, a second has an 11 aa substitution for aa 1-118, and three others show variable substitutions over aa 1-35. Over aa 119-289, human MITF-A1 shares 96% aa identity with mouse MITF-A1.