Like the Lambda repressor, the cII protein is a transcriptional activator. It binds to a site upstream of a promoter called PRE (for repressor establishment) and stimulates transcription of the cI (repressor) gene from that promoter.

TLS Online TPP Program

#Id: 6292

#Unit 3. Fundamental Processes

The carboxy-terminal domain of the a subunit (aCTD) recognizes the Up-element (where present), whereas s regions 2 and 4 recognize the –10 and –35 regions

TLS Online TPP Program

#Id: 6293

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6294

#Unit 3. Fundamental Processes

In holoenzyme Region 1.1 of s is highly negatively charged hence region 1.1 acts as a molecular mimic of DNA

TLS Online TPP Program

#Id: 6295

#Unit 3. Fundamental Processes

An additional DNA element that binds RNA polymerase is found in some strong promoters, for example, those directing expression of the ribosomal RNA (rRNA) genes. This is called an UP-element and increases polymerase binding by providing an additional specific interaction between the enzyme and the DNA.

TLS Online TPP Program

#Id: 6296

#Unit 3. Fundamental Processes

The start point is usually (90% of the time) a purine. It is common for the start point to be the central base in the sequence CAT, but the conservation of this triplet is not great enough to regard it as an obligatory signal.

TLS Online TPP Program

#Id: 6297

#Unit 3. Fundamental Processes

Down mutations to decrease promoter efficiency usually decrease conformance to the consensus sequences, whereas up mutations have the opposite effect.

 Mutations in the -35 sequence can affect initial binding of RNA polymerase.

Mutations in the -10 sequence can affect binding or the melting reaction that converts a closed to an open complex.