Gene regulation in prokaryotes/Review

Question 1: The Arabinose Operon

Part A

Like the products of the lac operon, the products of the ara operon degrade a sugar so it can supply energy for the cell. From this knowledge, would you expect the ara to be repressible or inducible? Explain

Part B

AraC is required both as an activator and a repressor. Which activity is favored in the presence of arabinose? Explain.

Part C

When araC mutants were first anaylzed, people concluded that AraC protein acts as an activator, not a repressor. Explain why they came to this conclusion.

Part D

What effect, if any would be the effect of deleting the araO₂ sites where AraC binds?

Part E

Explain how the presence of glucose will affect expression of the ara operon. Be specific!

Question 2: The Lac Operon

Part A

For each of the E. coli diploids that follow, indicate whether the strain is inducible, constitutive or negative for β-galactosidase and permease.

i^-o⁺z^-y⁺/i^-o^cz⁺y^-

i⁺o⁺z⁺y⁺/i^-o^cz⁺y^-

Part B

Suppose you have isolated a Lac^- mutant and by genetic analysis have found that the cell is z⁺y⁺; you have also found that the mutation, which you call i*, is in the i gene. The diploid i*o⁺z⁺y⁺/i^-o⁺z⁺y⁺ is constructed and found to be Lac^-

Is i* dominant or recessive?

The diploid i*o⁺z⁺y⁺/i⁺o^cz⁺y⁺ is Lac⁺. Suggest a property of the mutant repressor that would explain this phenotype. Explain your answer.

Would i*o⁺z⁺y⁺/i⁺o^cz^-y⁺ make β-galactosidase? Explain.