Positive Control of Transcription

Positive Control of Transcription

Positive Control of Transcription
This type of control has been recognised only during last ten years. Here the initiation of transcription is dependent upon the binding of the regulator to the promoter. Examples are many, as 0) the catabolite repressor protein (CRP) where CRP forms an active complex with cyclic AMP (CAMP), which acts on many different operons to increase the rate of their transcription (over 20'0 genes are regulated by CRP. CAMP complex in E. coli ). This is called global regulatory system as it affects genes of many different metabolic systems. (ii) specific regulator, the one which is specific to only one operon or group of operons.

When a number of operons are under the control of a single specific regulator it is termed a regulon. An example of this type is the arabinose regulation of E. coli.Regulation of gene expression usually requires the presence of another molecule other than the protein produced by the regulator gene. This is usually either the inducer or the repressor depending on its mode of action and the processes of regulation are known as induction or repression respectively. Both can be found in either negative or positive regulatory systems.

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