Fig 6.

Model for the induction of yeast GAL genes. (A) In the absence of galactose, Gal3p and Gal80p are produced at relatively low levels in the cell, and both proteins may be found in the nucleus and cytoplasm. (B) Galactose entering the cell promotes an interaction between Gal3p and Gal80p. This association occurs, at least in part, at the location of Gal4p and results in the expression of the GAL genes. (C) As Gal1p is produced and accumulates to a high level, the complex between Gal3p and Gal80p is disrupted and replaced by a complex between Gal1p and Gal80p. The Gal1p-Gal80p interaction occurs at the location of Gal4p.