Molecular structure of the Gal4p activator protein. It consists of two Gal4p, bound to a GAL upstream activator sequence (UAS). Space filling model representation showing the DNA backbone in yellow and purple and different parts of the Gal4p in orange and green. The orange regions form specific contact with the DNA. Gal4p, a member of a fungal trans-activator family, regulates transcription of genes controlling metabolism of galactose and galactose disaccharides like lactose in yeast.