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tata binding protein

molecular biology

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tata binding protein

  1. 1. TATA BINDING PROTEINS Presented by: Pragya Prasanna PhD Biotechnology
  2. 2. Transcription in Eukaryotes • Eukaryotic RNA polymerases, unlike their bacterial counterparts, are incapable of binding by themselves to their respective promoters • Eukaryotic RNA polymerases rely on proteins called transcription factors to show them the way • Two classes: general transcription factors and gene-specific transcription factors (activators)
  3. 3. • General transcription factors combine with RNA polymerase to form a preinitiation complex • The assembly of preinitiation complexes involving polymerase II is quite complex
  4. 4. 11-4 Model of Formation of the DABPolF Complex
  5. 5. Structure and Function of TFIID TFIID contains several subunits – TATA-box binding protein (TBP) • Highly evolutionarily conserved • Binds to the minor groove of the TATA box –Saddle-shaped TBP lines up with DNA –Underside of the saddle forces open the minor groove –The TATA box is bent into 80° curve – TBP-associated factors (TAFs) specific for class II
  6. 6. TBP [TFIID] function • Binds TATA - main sequence recognition event during Binds a variety of different TATA-like sequences – A slow binding reaction – minor groove contact – binds as monomer • Affinity of TBP for TATA contributes to promoter strength • Binds also several other polypeptides – activators (Sp1, Tax1, E1A) – TAFs (dTAF110, dTAF40) – GTFs (TFIIB, TFIIA) – inhibitors • TBP = universal TF involved in all three pol syst. – TBP i SL1, TFIID, TFIIIB DNA Other factors N
  7. 7. TBP versus TFIID • Subunit-structure – TFIID = TBP + multiple TAFs – mammalian TFIID: 750 kDa (II), 300 kDa (III) and 200 kDa (I) – TBP only a small core in the TFIID complex • human 38 kDa, yeast 27 kDa, Arabidopsis 22 kDa – TBP = N-term divergent domain + C-term. conserved domain • C-term domain 180aa • Carries all essential functions • N-term domain divergent TAFs TBP N
  8. 8. TBPs saddle-structure DNA protein Concave inside Convex surface 3D: saddle-structure • Twofold symmetry -form of a saddle. • Concave inside binds DNA in minor groove through a 10-stranded antiparallel -sheet • Convex surface binds other GTFs via 4 -helixes • loop (“stirrup”) on each side with Phe side- chains intercalating in DNA
  9. 9. TBPs effect on DNA • DNA-structure is distorted upon TBP binding – DNA severely bended, unwinded and distorted – DNA shaped by TBP´s -sheet – The intercalating Phe-residues contributes to kink • Effect? – Upstream and downstream elements brought closes together – incompatible with nucleosome structure .. but this way Not like this
  10. 10. A Two-Step Mechanism of TBP Binding to DNA • First step – Full-length TBPWT first binds to TATA box to form an unbent TBP-TATA box complex. • Second step – Then, this unbent complex slowly forms the bent TBP- TATA box complex. – TFIIB can directly recognize the unbent and/or bent TBP-TATA-complexes to form the bent TBP-TATA box complex.
  11. 11. 11-11 The Versatility of TBP • Genetic studies have demonstrated TBP mutant cell extracts are deficient in: – Transcription of class II genes – Transcription of class I and III genes • TBP is a universal transcription factor required by all three classes of genes • Required in transcription of at least some genes of Archaea, single-celled organisms lacking nuclei
  12. 12. Thank You

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