Mutations in the indicated genes of the lac operon | Homework Helpers

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)