GAL80

GAL80 is a regulatory protein in the budding yeast Saccharomyces cerevisiae that modulates the galactose-inducible GAL gene cluster. It functions as a negative regulator by binding to the GAL4 transcriptional activator and repressing expression of GAL1, GAL7, and GAL10.

In the absence of galactose, GAL80 associates with GAL4, blocking GAL4’s activation domain and preventing recruitment of the transcriptional machinery to GAL gene promoters. This repression keeps galactose metabolism genes turned off when the preferred carbon source is available.

Upon galactose availability, the sensor GAL3 binds galactose and ATP to form a complex that interacts with GAL80. This interaction relieves GAL80-mediated repression, allowing GAL4 to activate transcription of the GAL genes. The resulting expression enables the utilization of galactose as a carbon source.

Genetic regulation of this system centers on the GAL regulon, which comprises GAL4, GAL80, and GAL3. Expression of the GAL genes is also influenced by carbon sources through glucose repression, which can suppress GAL gene activation even when GAL3-GAL80 signaling would otherwise relieve repression.

Structure and research uses: GAL80 is a cytoplasmic protein that binds GAL4 but does not bind DNA on its own. In genetics and synthetic biology, GAL80 is used to modulate GAL4-driven expression, enabling inducible regulation and the construction of regulatory circuits in yeast and, in modified forms, in other model organisms.