Eukaryotic specific transcription factors Flashcards
What is the mediator complex?
Large conserved complex of 30+ proteins which allows basal level of transcription (neither induced not repressed)
-works with general transcription factors
How is a basal level of transcription maintained?
By mediator complex and general transcription factors
-Can be repressed or stimulated by specific transcription factors (repressors or activators)
How can regulons be identified?
Transcriptional profiling
-Using microarrays (to determine relative abundance of transcripts)
What is a regulon?
Set of genes coordinately regulated by the same sTFs
-genes within same regulon show same pattern of increased/decreased transcription
In eukaryotes!
eg. Galactose-regulated genes in yeast
What is the GAL gene switch?
Yeast regulon system for galactose metabolism
Expression regulated by:
-transcriptional activator Gal 4 (binds to UAS of galactose-regulated genes) -activates when galactose present
-transcriptional repressor Gal 80 (binds to Gal4 activation domain, blocking transcription activation and binds to Gal3 in cytoplasm) -when no galactose present
-Gal3 (depletes Gal80 nuclear pool to allow Gal4 to operate)
What is the typical structure of transcription factors?
Modular
-With DNA-binding domain and activation/repression domain(s) separated by flexible regions
eg. Gal4 (DNA-binding domain at N-term and activation domain at C-term)
How does yeast 2-hybrid assay analyse transcription factors?
Uses their modularity
Analyses protein-protein interactions
-Domains of tf fused to distinct proteins
-Can observe whether proteins interact to reconstitute tf function (eg. promote transcription)
How do transcription factors function as homodimers?
Recognise same sequence
How do transcription factors function as heterodimers?
Recognise different or same seq
-diff seqs increases no. potential transcription sites
How is transcription controlled combinationarily?
Can combine tfs as homo or heterodimers
-Broad diversity of combos to regulate!
Both coactivators and corepressors can function together
-Can have a range of responses rather than just on or off -responsive!
Name some examples of DNA binding domains
(in sTFs)
-Homeodomain fold
-Leucine zipper
-Zinc finger
What is the homeodomain fold?
DNA-binding domain where recognition helix interacts with major groove of DNA
-has similar structure to helix-turn-helix motif in prokaryotes.
-Encoded by Hox genes (involved in A/P development)
What are basic leucine zipper proteins?
Class of TFs containing extended amphipathic alpha helices to form a coiled-coil dimer structure
(Leu zipper = Leu residue at every 7th position)
-End of coiled-coil contains a recognition helix, rich in basic aas which bind to DNA
eg. Gal4, the activator in yeast GAL gene switch
What is the zinc finger domain?
Beta, beta, alpha fold around a central Zn2+ ion
-v. common in DNA binding domains and TFs
2 classes in sTFs: C2H2 (bind as monomer to DNA) or C4 (bind as dimers to DNA; have 2 Zn fingers)
What is the RNA recognition motif (RRM)?
RNA-binding domain in RNA-binding proteins made up of beta sheet supported by alpha helices
Binding to RNA mediated by stacking of hydrophobic residues and H-bonding between stack and phosphodiester backbone of RNA
