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Transcription Factors … (TF)

Transcription Factors … (TF). Transcription in eukaryote -controlled by trans-acting protein … TF -more complex than in prokaryotes. Transcription Factors … (TF). TF Binding at cis-acting regulatory sequences Can be repressosr ar activators Located much farther from promoter

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Transcription Factors … (TF)

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  1. Transcription Factors…(TF) Transcription in eukaryote -controlled by trans-acting protein…TF -more complex than in prokaryotes

  2. Transcription Factors…(TF) TF Binding at cis-acting regulatory sequences Can be repressosr ar activators Located much farther from promoter 10-100 kb up/down stream Alternative controlled

  3. Alternative controlled Transthyretin (TTR)..steroid hormone transporter 2 control elements 1.85-2.okb upstream element 200 bp upstream Turn the gene on in two different cell types hepatocytes choroid plexus cells

  4. How to get the gene of TF • Detection of the controlled elements…5’ deletion assay • Biochemical isolation of TF • -several chromatographic steps with cell extract • …....get cognate proteins • -Dnase footprint or mobility shift assay • …....get specific DNA binding proteins • -sequence-specific DNA affinity chromatography • …...get a purified protein • In vivo transcription activation…to confirm protein function • Partial amino acid sequence determination and gene cloning • In vivo assay of the TF gene activity

  5. Detection of the controlled elements 5’-deletion analysis +++ +++ + + -

  6. Several chromatographic steps with cell extract …get cognate proteins fractions collected Retardation assay Dnase footprint DNase footprint/mobility shift assay

  7. Biochemical isolation of TF DNase footprint assay Interesting fractions = 9-12

  8. Mobility shift assay Gel retardation assay Biochemical isolation of TF

  9. Sequence-specific DNA affinity chromatography …...get a purified protein fractions 9-12 Specific regulatory sequence purified protein In vivo transcription activation assay

  10. In vitro transcription activation…to confirm protein function SP1 binding site in SV40 genome No SP1 binding site on adenovirus SP1 protein has no effect on transcription from the adenovirus promoterbut stimulate transcription from SV40 promoter about 10 folds. SP1 RNA- + - +

  11. isolated TF partial protein sequences oligonucleotide probe TF gene

  12. To test the gene function….in vivo assay

  13. General structure of TF Study by in vitro translation and N-terminal deletion assay 2 functional domains found UAS = upstream activating sequence

  14. General Structure of TF 2 functional domains DNA –binding domain…interact with specific DNA sequence Activation domain…interact with other proteins

  15. 5 structural types of DNA binding domain • Homeodomain (helix-turn-helix) • Zinc-finger protein • Winged-helix (fork-head) • Leucine zipper • Helix-loop-helix

  16. Homeodomain ( helix-turn-helix ) • The name derived from a group of Drosophila genes in which the conserved sequence encoding this structural domain was first noted. • Homeotic genes, mutation in these genes resulted in the transformation of one body part into another during the development. • Two of most-studied of these genes • Antennapedia (Antp) • Ultrabithorax (Ubx) normal fly mutant fly

  17. Structure of homeodomain

  18. Helix-Turn-Helix protein and Homeoboxes -Three -helical regions separated by short turns. -Bind to DNA in similar manner. -Bind as dimers -Amino acid substitution in the  helices near C terminal disturb the binding in major groove of DNA -The region encoding about 60 amino acids was remarkably conserved in all these genes called homeobox. Homeobox = region in the gene Homeotic gene = gene Homeodomain / helix-turn-helix protein = protrein encoded by homeotic gene

  19. Example of helix-turn-helix proteins Gene product Organism Functions MAT 1 yeast activates -specific genes MAT 2 yeast inactivates a-specific genes MAT a1 yeast combined with 2 repressed haploid-specific genes Antennapedia Drosophila homeotic gene Ultrabithorax Drosophila homeotic gene Engrailed Drosophila segment-polarity gene Paired Drosophila pair-rule gene Fushi tarazu Drosophila pair-rule gene HOX mouse developmental regulators Unc86 C. elegans determine cell lineage in worms Oct1 human generally distributed activator Oct2 human lymphoid-specific activator Pit mouse pituitary-specific activator

  20. Determine the fate of each segments (mouth, legs, wings,etc.)

  21. The 9 homeotic genes in fly Bithorax complex (Bx-C) Ultrabithorax (Ubx) Abdominal A (abdA) Abdominal B (abdB) Antennapedia complex (Ant-C) labial (lab) Prodoscipedia (pb) Deformed (Dfd) Sex combs reduced (Scr) Antennapedia (Antp) Engrailed

  22. Example of homeotic genes in mouse and human Pit-1 mutant Growth hormone deficiency

  23. Example of homeotic genes in plant 3 classes of floral organ-identity genes in Arabidopsis, A B and C, encoded TF of MADS family

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