Domains in Transcription Factors
- Dimerization domains
- DNA-binding domains
- Activation Domains
- similar, but different protein
- protein-protein interactions -
- protein-DNA interactions
- bind to DNA in sequence specific manner.
- Must be a pair of DNA binding domains in the correct conformation by dimerization of protein
- protein-protein interactions
- activate transcription or prevent transcription (gene silencing)
Leucine Zippers in bZIP Transcription Factors
- protein-protein domain
- Leucine at 1, 8, 15, 22 forms hydrophobic face. Two helices form a dimer based on hydrophobicity
- acts like a zipper to make 2 dimerization domains interact
- transcription factor
- ZIP - Zipper Dimerization Domain
- b - basic (positively charged) DNA-binding domain.
- basis for interactions of negatively charged DNA
Leucine Zippers and DNA
- zipper is dimerization domain
- b-DNA binding domain
- activation domain
- to interact with all other proteins. located in C-terminal region.
Helix-Loop-Helix Transcription Factors b/HLH
- variation of leucine zipper.
- dimerization puts DNA binding domain into correct spot to bind alpha helix due to high content of basic AA - weak chemical interactions
- AA in loops act non-specifically with phosphate of DNA backbone (not dependent on sequence of DNA)
- due to ionic and hydrogen bonds between the R groups of the amino acids and information in the major groove of DNA.
- DNA binding domains
- 2 cysteines (on right) , 2 histidines (on left)
- Both secondary structures represented in zinc finger
Tandem Repeats of Zinc Fingers
- rare to have single zinc fingers in a protein
- multiple fingers needed to interact strongly with DNA
- multiple contacts good fit
- identity of AA determine specificity of DNA binding
- TF - transcription factor
- III - RNA pol III
- A - first discovered
- uses zinc fingers to place genes and traits
- each additional zinc finger increases specificity.