Although there are many different Transcription Factors in any given organism - there are more than 1,800 in humans - and each has a specific binding site that it recognizes, there are some structural features that occur quite commonly across all of these proteins. This is due to their shared ancestry and although they have diverged in specialized function over evolutionary time, the common ancestry is apparent in the common structural motifs. Some common structural motifs that are found in the DNA-Binding Domain of transcription factors are:
- Helix-turn-helix: This is a motif found in, among others, the well-studied Homeodomain proteins (coded by Hox genes) that regulate aspects of animal development. The motif consists of two alpha-helices in the protein separated by a short stretch of amino acids (the "turn"). The alpha helices form the DNA-binding domain of the transcription factor that has this motif.
- Helix-loop-helix: Similar in structure to the Helix-Turn_Helix, this motif has two alpha helices separated by amino acids that loop out. This generates a different angle between the helices so that the overall structure is somewhat different. This is also the DNA-Binding domain of the transcription factor.
- Zinc finger: A complex structure in which a stretch of amino acids form what looks like a finger. This is the DNA-Binding domain of the transcription factor.
The Wikipedia page on Transcription Factors
