Functional Requirements for Repressors and Transcriptional activators

Regulatory DNA-binding proteins are multi-fimctional. Aside from their DNA-binding property, they also have the ability to register regulatory signals and transmit the signals on to the transcription apparatus. (Fig. 1.21). 

The DNA-binding protein must be capable of transmitting signals to the transcription apparatus via protein-protein interactions. DNA-binding alone can be ascribed the function of increasing the effective concentration of the transcription regulator at the site of the transcription apparatus. 

Regulatory signals should only be effective for a limited period of time and imder certain external conditions. This also holds, of course, for regulation at the transcription level. It is therefore necessary to turn off the transduction of signal by the DNA-binding protein after the mediated demands have been fulfilled. Cells use common mechanisms for both the activation and inactivation of signal pathways. These are summarized below. 

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