Transcription Factor Binding Domains

All of the eukaryotic RNA polymerases require additional protein factors--transcription factors-- to bind to a promoter and initiate transcripition. A typical transcription factor will contain a DNA-binding domain and one or more regulatory domains, which can interact with other nuclear proteins to convey regulatory signals.

In addition to the zinc-finger proteins, two other major classes of transcriptional factors are recognized, and these are depicted schematically in Figure 28.23. In the helix-turn-helix proteins, one helix (called the recognition helix) lies in the major groove of the DNA, its side chains making specific contacts with the DNA bases.

The leucine zipper proteins, on the other hand, are a quite different class of DNA-binding proteins. The leucine zipper proteins are dimers, held together in a coiled-coil structure by hydrophobic interactions. They typically exhibit a regular pattern (7-fold periodicity) of leucine or other hydrophobic residues in the helical tail regions, which favors side-by-side hydrophobic interactions. The N-terminal regions are recognition helices, lying in adjacent major grooves. Leucine zipper proteins can form either homologous or heterologous dimers, thus allowing many combinatorial combinations in transcription factors.

See also: Eukaryotic Transcription, RNA Polymerase I Transcription, RNA Polymerase III Transcription, RNA Polymerase II Transcription

INTERNET LINKS:

> 1. Transcription Factor Database

> 2. TFIIB Structure

> 3. Eukaryotic Promoter Database

> 4. Nucleic Acid - Protein Binding Motifs (slow)