The origin of E. coli, oriC, is 245 bp in length. The genome of E. coli is replicated bidirectionally from a single unique site called the origin, identified as the genetic locus oriC.

Two replication forks initiate atoriCand move around the genome at approximately the same speed to a special termination region.

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#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.

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#Unit 2. Cellular Organization

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

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#Unit 2. Cellular Organization

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

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#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.

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#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.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.

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#Id: 6390

#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.