The GAL gene system in yeast is used to metabolize galactose. In the presence of galactose, the GAL genes are expressed; however, in the absence of galactose, the GAL genes are repressed.

A yeast mutant is discovered that continuously expresses the GAL genes in the presence or absence of galactose. Which GAL gene is likely mutated?

Saccharomyces cerevisiae is a yeast. Gal4 and Gal3 are the two binding partners of the Gal80 protein. Gal80 binds to and inhibits the transcriptional activation domain (AD) of the GAL gene activator, Gal4, inhibiting the expression of the GAL gene in the absence of galactose. Thus, GAL80 is the gene that is likely to get mutated that alters galactose metabolism.

GAL80 is the logical off-switch if GAL4 is the typical on-switch for almost any desirable transgene. By attaching to the GAL4 transcriptional activation domain, GAL80 prevents RNA polymerase recruitment. Gal80 is taken out of the Gal4-activation domain upon galactose induction, allowing it to activate the transcriptional machinery. Gal4 that is transcriptionally active is subject to Dsg1 regulation.

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Complete question is:

The GAL gene system in yeast is used to metabolize galactose. In the presence of galactose, the GAL genes are expressed; however, in the absence of galactose, the GAL genes are repressed. A yeast mutant is discovered that continuously expresses the GAL genes in the presence or absence of galactose. Which GAL gene is likely mutated?

A) GAL4

B) GAL180

C) GAL3

D) GAL1

E) GAL 10