Question

Consider the regulation of galactose metabolism through GAL4. GAL4 binds to a UAS sequence to activate gene expression, but this activation is repressed by GAL80. Normally, in the presence of galactose, GAL3 removes GAL80 from GAL4. Which of the following would result from a mutation that caused GAL80 to be absent?

a. Transcription of the target genes would always occur.
b. Transcription of the target genes would never occur
c. Transcription of the target genes would only occur in the presence of galactose.
d. Transcription of the target genes would only occur in the absence of galactose.

Answer 1

Without GAL80 due to a mutation, GAL4 remains active, leading to constant transcription of the galactose metabolism genes regardless of the presence of galactose. Therefore correct option is A

Step-by-step explanation:

If there is a mutation that causes GAL80 to be absent in the regulation of galactose metabolism, transcription of the target genes would always occur. This is because GAL80 normally represses GAL4 by binding to it and preventing it from activating transcription. In the presence of galactose, GAL3 relieves this inhibition by removing GAL80 from GAL4, permitting transcription. Without GAL80, GAL4 would remain unbound, constantly active and able to promote transcription of the galactose-utilizing genes regardless of the presence or absence of galactose. Hence, the correct answer to the effect of a GAL80 absence is that the transcription of the target genes would always occur.