11.4 - Combinatorial control in eukaryotes

Question 1

What is the upstream activating sequence?

Answer 1

• The equivalent in yeast of the enhancer in higher eukaryotes
  that is bound by transcriptional activator proteins; a UAS cannot
  function downstream of the promoter

Question 2

What are the 5 levels of regulation of GAL genes?

Answer 2

1. Chromatin opening (SWI/SNF, acetylation)
2. Non-coding RNA transcripts
3. UAS has both enhancer and Mig1 repressor binding sites
4. GAL-specific induction system
5. Catabolite repression

Question 3

Describe the Yeast GAP genes: Model for Activation and Repression

Answer 3

GAL1/10 genes are positively regulated by the activator Gal4.
•GAL1/10 genes are negatively regulated by a noncoding RNA synthesized from a cryptic promoter that controls chromatin structure.

Question 4

GAL genes

Answer 4

•GAL1 is transcribed to the right
- promoter region is 118 bp long and contains 4 upstream activator sites (UAS)

•GAL10 is transcribed in the opposite direction from the same control region

•UAS bind DNA-binding trans-activator protein made by GAL4 gene –

Question 5

Describe the process for turning on GAL genes

Answer 5

Need Gal4p – transcription activator – needed to bind to RNA polymerase to start transcription of genes so cell can use galactose
•involves additional proteins besides GAL4p
•The inhibitor –
•Ligand sensor –
•Mig1 –presence in nucleus dependent on phosphorylation – dependent on absence of glucose
•Tup1 – binds to Mig1 – blocks transcription