Which of the following statements is accurate regarding the regulation of gal genes in yeast?

• A. Gal4p activates transcription of gal genes only in the presence of galactose.
• B. Gal80p acts as a transcriptional activator for gal gene expression.
• C. In the absence of galactose, Gal4p is degraded by the proteasome.
• D. Gal3p represses gal gene expression by binding directly to DNA.

Answer: (A)

Verified step by step guidance

1. Understand the roles of the key proteins involved in the regulation of gal genes in yeast: Gal4p, Gal80p, and Gal3p.
2. Recall that Gal4p is a transcription factor that binds to the upstream activating sequences (UAS) of gal genes to promote their transcription.
3. Know that Gal80p acts as a repressor by binding to Gal4p and preventing it from activating transcription when galactose is absent.
4. Recognize that Gal3p functions as a sensor of galactose; in the presence of galactose, Gal3p interacts with Gal80p, causing Gal80p to release Gal4p, thereby allowing transcription activation.
5. Conclude that the accurate statement is that Gal4p activates transcription of gal genes only in the presence of galactose, while Gal80p represses transcription and Gal3p relieves this repression indirectly, not by binding DNA or repressing directly.