Gene regulation in prokaryotes/Review
Question 1: The Arabinose Operon
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
AraC is required both as an activator and a repressor. Which activity is favored in the presence of arabinose? Explain.
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.
What effect, if any would be the effect of deleting the araO2 sites where AraC binds?
Explain how the presence of glucose will affect expression of the ara operon. Be specific!
Question 2: The Lac Operon
For each of the E. coli diploids that follow, indicate whether the strain is inducible, constitutive or negative for β-galactosidase and permease.
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+ocz+y+ is Lac+. Suggest a property of the mutant repressor that would explain this phenotype. Explain your answer.
Would i*o+z+y+/i+ocz-y+ make β-galactosidase? Explain.