Question

Understanding regulation of transcription in eukaryotes. The images below depict how the expression of a gene required to break down lactose in yeast is regulated. The top image illustrates the key regulators of the process. The bottom two panels illustrate what happens in the presence and absence of galactose. Describe how the expression of this gene is regulated. Include the roles of all key players illustrated below in this process. Key players in the process GAL4 GALS GALBO UAS WAS Gene promoter Coding sequence RNA polymerase Transcription factors Galactose present: No galactose: GAL3 — GAL4 WAS GALA UAS -GALBO GAL80 GAL3 TATA Galactose Basal transcription apparatus

What would happen to the expression of this gene if this cell did not have any GAL4 protein and why?

What would happen to the expression of this gene if this cell did not have any GAL80 protein and why?

What would happen to the expression of this gene if this cell did not have any GAL3 protein and why?

Answer 1

What would happen to the expression of this gene if this cell did not have any GAL4 protein and why?

GAL4 is a positive regulator of the genes which are induced under galactose. Here in the presence of Galactose GAL80 is inactivated by GAL3 so that GAL4 can interact with transcription factors to help initiate transcription by RNA polymerase. So in the absence of GAL4 protein the expression of this gene will be reduced or blocked even in the presence of galactose.

What would happen to the expression of this gene if this cell did not have any GAL80 protein and why?

GAL80 is a negative regulator of GAL4 protein which prevents GAL4 from activating the expression of this gene in the absence of galactose. Only when Galactose is present will GAL80 be inactivated by GAL3 so that GAL4 is free to interact with the transcription factors involved in the transcription of this gene. So in the absence of GAL80 this gene will be expressed even in the absence of galactose.

What would happen to the expression of this gene if this cell did not have any GAL3 protein and why?

GAL3 protein is there to inactivate GAL80 in the presence of galactose so that GAL4 is free to interact with the transcription factors to initiate transcription of this gene by RNA polymerase. So if GAL3 is not present GAL80 will be bound to GAL4. So even in the presence of galactose this gene expression will be reduced or blocked.