Predict the lacZ and lacY expression when lactose is present/absent.
Understanding the symbols:
A* wild type with normal function
A mutant without normal function => No expression
A always ON => not respond to other elements
A S: always OFF => not respond to other elements
rP*OZ*Y/I*p*O*ZY
Here is a solution step for this question:
1. Cross all the non-working elements
2. Does this E. coli have active repressor gene(s)?
3. Does this E. coli produce active repressor proteins? If yes, which one?
4. Consider whether the components of lac operon look okay - Promoter: P* vs. P
5. Consider whether the components of lac operon look okay - Operator: O* vs. O
6. If there is no lactose, which enzyme(s) will be produced in this E. coli?
7. If there is enough lactose, but no glucose, which enzyme(s) will be produced in this E. coli?
8. Summary of 1st operon and 2nd operon:
Predict the lacZ and lacY expression when lactose is present/absent.
Lactose absent
1st operon 2nd operon
IP+OZY+/rP+O+ZY
B-galactosidase B-galactosidase (yes/no) (yes/no)
Permease Permease (yes/no) (yes/no)
rPOZY/I+P+OZ+Y
B-galactosidase B-galactosidase (yes/no) (yes/no)
Permease Permease (yes/no) (yes/no)
SPO+ZY/IP+OZY
B-galactosidase B-galactosidase (yes/no) (yes/no)
Permease Permease (yes/no) (yes/no)
Lactose present
1st operon 2nd operon
B-galactosidase B-galactosidase (yes/no) (yes/no)
