Marker position 

TLS Online TPP Program

#Id: 577

#Unit 2. Cellular Organization

Promoter mutations are also cis-acting. If they prevent RNA polymerase from binding at P-lac, the structural genes are never transcribed.

TLS Online TPP Program

#Id: 578

#Unit 2. Cellular Organization

Mutants that cannot be expressed at all are called uninducible. Mutants that are continuously expressed are called constitutive mutants.

TLS Online TPP Program

#Id: 579

#Unit 2. Cellular Organization

“Cryptic mutants” of lac operon make b-galactosidase but still could not grow on lactose means they are essentially Y-

TLS Online TPP Program

#Id: 580

#Unit 2. Cellular Organization

Catabolite repression is exerted through a second messenger called cyclic AMP (cAMP) and the positive regulator protein called the catabolite repressor protein (CRP), a dimer.

TLS Online TPP Program

#Id: 581

#Unit 2. Cellular Organization

CAP–cAMP complex stimulates transcription of the lac operon by binding to an activator-binding site adjacent to the promoter and helping RNA polymerase bind to the promoter.

TLS Online TPP Program

#Id: 582

#Unit 2. Cellular Organization

CAP–cAMP increases the rate of formation of the closed promoter complex, CAP–cAMP provides CPC for conversion to the open promoter complex. 

Thus, the net effect of CAP–cAMP is to increase the rate of open promoter complex formation.