Question

What would the difference be between a lac repressor null mutation and a CRP activator null mutation on E. coli B-galactosidase production in the presence and absence of lactose? Use a table to illustrate your answer.

Answer 1

The effect of lac repressor null mutation

the opron will become constitutive. So the beta galactosidase production will be constitutive either lactose is present or not.

Because inactivated lac repressor can no longer bind to the operator site of operon.

effect of CRP activator null mutation

Operon will be turned OFF always (even in the presence of lactose)

CRP protein is required because it recruits RNA polymerase to the promoter sit of lac operon. without CRP RNA pol. Cannot bind and transcription of lac genes will not occt.

But CRP required to be activated by cAMP molecule. If there is no cAMP, CRP will not be activated thus operon will be turned OFF.