Consider the following mutations in the indicated genes of the lac operon. Given the growth conditions listed, predict the relative rate of transcription of the operon in each case. Answer OFF or ON, and if you answer ON, say if the transcription rate would be LOW, or HIGH, as appropriate.
Case Mutation: Lactose Glucose Rate of lac mRNA transcription
A Is, Oc absent high ?
B I–d , PDE– absent high ?
C Oc, AC– present low ?
D I–, CAP–, PDE– absent low ?
E Is, CAP–, AC– present high ?
Mutant definitions (null mutation means that no product of the gene is made):
I– = repressor minus (null mutation)
I–d = cannot bind to operator
Is = super-repressor (cannot bind to inducer)
Oc = operator constitutive
CAP– = catabolite activator protein minus (null mutation)
AC– = adenylate cyclase minus (null mutation)
PDE– = cAMP phosphodiesterase minus (null mutation)