Transcription factor

In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. Transcription factors can be selectively activated or deactivated by other proteins, often as the final step in signal transduction.

Classes

There are three classes of transcription factors:

• General transcription factors are involved in the formation of a preinitiation complex. The most common are abbreviated as TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH. They are ubiquitous and interact with the core promoter region surrounding the transcription start site(s) of all class II genes.
• Upstream transcription factors are unregulated proteins that bind somewhere upstream of the initiation site to stimulate or repress transcription.
• Inducible transcription factors are similar to upstream transcription factors but require activation or inhibition.

Motifs found in transcription factors

• Helix-turn-helix (HTH) bind the major groove of the DNA.
• Zinc fingers function as structural platforms for DNA binding.
• Leucine zippers function in associating the transcription factors with each other.
• Basic-helix-loop-helix (bHLH) bind DNA with two alpha helices containing basic amino acid residues which are linked by a loop and are typically dimeric.

See also

• DNA-binding protein

• TFIIA
• TFIIB
• TFIID
• TFIIE
• TFIIF
• TFIIH