What role does GAL3 play when it binds to GAL80?

The role of GAL3 when it binds to GAL80 is best understood in the context of the GAL gene regulation system in yeast, specifically in response to galactose. When galactose is present, GAL3 binds to GAL80, which leads to a conformational change in GAL80. This change causes GAL80 to release its inhibition on GAL4, the transcriptional activator.

The correct answer indicates that GAL3 binding to GAL80 converts UASg (upstream activating sequence) into a silencer. However, while this reflects a misunderstanding of the regulatory process, the primary effect of GAL3 binding to GAL80 is to relieve inhibition. When GAL3 binds to GAL80, GAL80's inhibitory role is diminished, allowing GAL4 to activate transcription of downstream genes.

In the GAL system, UASg is where GAL4 binds to enhance transcription, and GAL3's action is crucial in removing the repression so that the genes needed to metabolize galactose can be expressed. Therefore, rather than inhibiting transcription or converting UASg to a silencer, GAL3's binding actually facilitates the transcription process by allowing GAL4 to activate target gene transcription when galactose is available. This makes the understanding of GAL3 and