Lecture Molecular biology (Fifth Edition): Chapter 11 - Robert F. Weaver

Chapter 11 - general transcription factors in eukaryotes. Eukaryotic RNA polymerases, unlike their bacterial counterparts, are incapable of binding by themselves to their respective promoters. Instead, they rely on proteins called transcription factors to show them the way. Such factors are grouped into two classes: general transcription factors and gene-specifi c transcription factors (activators). In this chapter we will survey the general transcription factors that interact with all three RNA polymerases and their promoters.
Nội dung trích xuất từ tài liệu:
Lecture Molecular biology (Fifth Edition): Chapter 11 - Robert F. WeaverLecture PowerPoint to accompanyMolecular Biology Fifth Edition Robert F. Weaver Chapter 11General TranscriptionFactors in Eukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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) 11-2 11.1 Class II Factors• General transcription factors combine with RNA polymerase to form a preinitiation complex – This complex is able to initiate transcription when nucleotides are available – Tight binding involves formation of an open promoter complex with DNA at the transcription start site that has melted• The assembly of preinitiation complexes involving polymerase II is quite complex 11-3 The Class II Preinitiation Complex• Class II preinitiation complex contains: – RNA Polymerase II – 6 general transcription factors: • TFIIA, TFIIB, TFIID, TFIIE, and TFIIH• The transcription factors (TF) and polymerase bind the preinitiation complex in a specific order (as studied in vitro) 11-4 Four Distinct Preinitiation Complexes• Transcription factors bind to class II promoters in the following order in vitro:• TFIID with help from TFIIA binds to the TATA box forming the DA complex• TFIIB binds next generating the DAB complex• TFIIF helps RNA polymerase bind to a region from -34 to +17, now it is DABPolF complex• Last the TFIIE then TFIIH bind to form the complete preinitiation complex = DABPolFEH• In vitro, the participation of TFIIA seems to be optional 11-5Model of Formation of the DABPolF Complex 11-6 Structure and Function of TFIIDTFIID 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 11-7Structure of the TBP-TATA box complex 11-8 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 11-9 The TBP-Associated Factors• These are also called TAFs (TAFIIs is written to denote transcription of class II genes)• 13 TAFs have been identified and associated with class II preinitiation complexes• The core TAFs were first named according to their molecular mass but have now been renamed according to their sizes, from largest to smallest• Several functions discovered: – Interaction with the core promoter elements – Interaction with gene-specific transcription factors – When attached to TBP extend the binding of TFIID beyond the TATA box 11-10Model for the Interaction Between TBP and Promoters 11-11 Roles of TAF1 and TAF2• The TAF1 and TAF2 help the TFIID bind to the initiator and DPE of promoters• They enable TBP to bind to TATA-less promoters that contain elements such as a GC box• Different combinations of TAFs are required to respond to variosu activators, at least in higher eukaryotes• TAF1 has two enzymatic activities: – Histone acetyltransferase (HAT) – Protein kinase 11-12Transcription Enhancement by Activators 11-13 Exceptions to the Universality of TAFs and TBP• TAFs are not universally required for transcription of class II genes• Even TBP is not universally required• Some promoters in higher eukaryotes respond to an alternative protein such as TRF1 (TBP-related factor 1)• The general transcription factor NC2: – Stimulates transcription from DPE-containing promoters – Represses transcription from TATA-containing promoters 11-14 Structure and Function of TFIIB• Structural studie ...