Regulatory Proteins

Positive Regulation

• The binding of specific protein (activator) is required for transcription to begin.

• DNA bound activators can regulate transcription by helping with ignition. To do this they sometimes tether RNA polymerase to the promoter.

Negative Regulation

• The binding of a specific protein (repressor) inhibits transcription from occurring.

• DNA bound repressors often act to prevent RNA polymerase from binding to the promoter, or by blocking the movement of RNA polymerase

In order to be effective, activators and repressors must be able to exist in 2 states

1)      able to bind to DNA

2)      unable to bind to DNA

both states must occur under appropriate physical conditions

Many activators and repressors are regulated through the allosteric site, which interacts with small molecules called allosteric effectors

• The binding of an allosteric effectors changes the shape of the DNA binding site making the regulatory protein:

                              a) Able to bind to DNA, activating transcription

                              b) Unable to bind to DNA, activating transcription