The GAL regulatory system refers to a set of mechanisms that control the expression of genes in response to specific signals. It is primarily studied in the model organism Saccharomyces cerevisiae, commonly known as yeast. This system allows researchers to understand how genes are turned on or off, which is crucial for cellular function and adaptation. In the GAL system, the presence of galactose activates a series of proteins that promote the transcription of genes necessary for galactose metabolism. This regulatory process involves key components such as GAL4, a transcription factor that binds to DNA, and GAL80, which inhibits GAL4 in the absence of galactose.