Transcription Factors

A significant mechanism of gene regulation in eukaryotes involves the action of proteins called Transcription Factors. A Transcription Factor is a protein that recognizes (i.e. binds to) a specific DNA sequence and, once bound to the DNA molecule, affects the rate of transcription initiation from a promoter that is near the binding site.

There are other proteins that can regulate gene expression but that are not referred to as Transcription Factors because they have a different mode of action - that is, the way in which they affect gene expression is different. Examples would include proteins that modify histones and proteins that methylate DNA. These mechanisms of gene regulation are discussed elsewhere.

The general way that Transcription Factors regulate gene expression is through the following steps, which are discussed in detail in the links below. Any protein that regulates expression by this general mechanism is called a Transcription Factor.

• First the Transcription Factor is activated. This occurs under specific conditions so that the resulting change in expression of the regulated gene is essentially a response to these conditions.


• Second, once it is activated the Transcription Factor can bind to a specific DNA sequence. A sequence that is bound by a Transcription Factor is referred to as a Transcription Factor Binding Site (TFBS).


• Third, once bound to the TFBS the Transcription Factor interacts with the Pre-Initiation Complex at the promoter or recruits other proteins that introduce epigenetic changes. Some Transcription Factors enhance transcription of the 'target gene' while others repress transcription of the 'target gene'. These actions lead to a change in gene expression level.
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Note: the Transcription Factors discussed here are different from the proteins that are called Basal Transcription Factors, also called General Transcription Factors (see Eukaryotic Transcription Initiation). Basal transcription factors, along with RNA Polymerase, make up the Pre-Initiation Complex (PIC) which forms at the promoter. The Transcription Factors discussed in this section are not part of the PIC, although they do interact with the PIC, and the TFBSs that we are discussing here are not considered to be part of the promoter.

The following links cover the basic structure and activation of Transcription Factors, the properties of TFBSs as well as the basic mechanisms of action - that is, how Transcription Factors regulate gene expression once they have been activated and are bound to DNA.

• Transcription Factor structure


• Transcription Factor activation


• Enhancers


• Mechanisms of action