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Overview of RNA Polymerase Function and Gene Transcription in E. coli and Eukaryotes

This chapter focuses on the central dogma of molecular biology, particularly the transcription process in E. coli and eukaryotes. It discusses the structure and function of the RNA polymerase enzyme, its subunits, and the importance of sigma factors in transcription initiation. The chapter further explores gene structures, including promoters and terminators, and highlights the differences between E. coli and eukaryotic RNA polymerases, such as transcription factors and the TATA box essential for transcription initiation in eukaryotic cells.

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Overview of RNA Polymerase Function and Gene Transcription in E. coli and Eukaryotes

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Presentation Transcript

  1. Chapter 21 (part 1) Transcription

  2. Central Dogma

  3. RNA Content of E. coli Cells

  4. E. Coli RNA Polymerase • RNA polymerase core enzyme is a multimeric protein a2,b, b’, w • The b’ subunit is involved in DNA binding • The b subunit contains the polymerase active site • The a subunit acts as scaffold on which the other subunits assemble. • Also requires s-factor for initiation –forms holo enzyme complex Site of DNA binding and RNA polymerization

  5. Promoter Transcribed region terminator 5’ 3’ General Gene Structure

  6. Gene Promoters

  7. Other s-Factors • Standard genes – s70 • Nitrogen regulated genes – s54 • Heat shock regulated genes – s32

  8. Transcriptional Initiation Closed complex Open complex Primer formation Disassociation of s-factor

  9. Pausing induces termination 3’end tends to be AU rich easily to disrupt during pausing. Leads to disassembly of RNA polymerase complex

  10. Rho Dependent Termination • rho is an ATP-dependent helicase • it moves along RNA transcript, finds the "bubble", unwinds it and releases RNA chain

  11. Eukaryotic RNA Polymerases

  12. Eukaryotic RNA Polymerases • RNA polymerase I, II, and III • All 3 are big, multimeric proteins (500-700 kD) • All have 2 large subunits with sequences similar to  and ' in E.coli RNA polymerase, so catalytic site may be conserved

  13. Eukaryotic Gene Promoters • Contain AT rich concensus sequence located –19 to –27 bp from transcription start (TATA box) • Site where RNA polymerase II binds

  14. Transcription Factors • TFAIIA, TFAIIB – components of RNA polymerase II holo-enzyme complex • TFIID – Initiation factor, contains TATA binding protein (TBP) subunit. TATA box recognition. • TFIIF – (RAP30/74) decrease affinity to non-promoter DNA

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