L16 Transcription in bacteria

L16 Transcription in bacteria - Credit: Irina Artsimovitch...

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Unformatted text preview: Credit: Irina Artsimovitch and Ohio State University) Transcription in bacteria 1 Last Time ✤Coordination of cell cycle and replication (bacteria) ✤Technique: Mutational analysis of DNA replication (bacteria) ✤Challenges in Eukaryotic DNA replication ✤More DNA ✤Linear chromosomes 2 Transcription in bacteria ✤ Overview of transcription ✤ Landmark sequences - recognizing patterns of sequence Three stages: Initiation, Elongation, Termination ✤ ✤ Specific mechanisms of bacterial transcription 3 From gene to protein (or RNA product) DNA ‘reverse transcription’ (RNA viruses) transcription RNA translation of mRNAs functional RNA (rRNA, tRNA) Protein 4 Replication vs. Transcription makes ss molecule rNTP, dNTPs, complementary to genome U T 1 strand of DNA affected template Transcription X X, using RNAP part Replication X X, using DNAP all 5 The organization of a gene: recognizing patterns of sequence Regulatory and other sequences on DNA Promoter Terminator Regulatory sequence 6 The organization of a gene: recognizing patterns of sequence Regulatory sequences on mRNA AUG CCC GAG UUU UAG ribosomal recognition sequence http://www.modares.ac.ir/elearning/Dalimi/Proto/Lectures/week2/ribosome_1%5B1%5D.gif http://www.cgl.ucsf.edu/chimera/ImageGallery/entries/rnabases/1s72-rna.png 7 a word on nomenclature…. “upstream” “downstream” 3’ 5’ RNA 3’ 3’ Template, non-coding strand 5’ -100 5’ -1 +1 Non-template, coding strand 8 Three stages of transcription 1. Initiation - RNA polymerase (RNAP) binds DNA, begins transcription 2. Elongation - RNAP continues to synthesize RNA 3. Termination - RNAP reaches termination sequence, mRNA transcript and RNAP dissociate from DNA 9 Initiation - overview promoter gene terminator 10 Elongation - overview promoter terminator 11 Termination - overview promoter terminator functional RNA (rRNA, tRNA) see Table 12.1 Protein 12 A closer look at initiation: Sequence patterns in bacterial promoters PROMOTER -35 box (16-18bp) template Pribnow box -10 box trx s n rt ta ite s 13 Correlation to consensus determines ‘strength’ of promoter (weak) (strong) 14 RNA Polymerase (RNAP) ✤DNA-dependent RNA Polymerase ✤polymerizes in the 5’ to 3’ direction ✤NTPs (ribose, not deoxyribose) added only to the 3’ end), PPi released ✤Base pairing of hybrid (DNA/RNA) follows Watson-Crick pairing rules, determined by template strand ✤A primer is not required, but does need double stranded DNA 15 E. coli RNA polymerase Holoenzyme αββ’ σ- 2 copies 1 copy 1 copy 1 copy Core 16 Looking up from below the DNA. Helix Loop Helix structure of sigma protein 17 Initiation RNAP scans for promoter region Closed complex (RNAP binds loosely) Open complex (RNAP binds tightly) *RNAP has higher affinity for ssDNA than dsDNA 18 Initiation 19 Elongation Direction of transcription 20 an important point about the direction of transcription….. 21 Termination - the end of the road ✤ Two mechanisms of termination: ✤ Rho (ρ) - Dependent termination ✤Rho is an RNA helicase! ✤ Rho (ρ) - Independent termination 22 Rho (ρ) - Dependent termination Rho recognition site Terminator terminator sequence of G-Cs 23 Rho (ρ) - Dependent termination Rho travels along RNA Hairpin forms Rho causes dissociation of RNAP and transcript from DNA 24 Rho (ρ) - Independent termination A-rich region stem loop NusA protein holds RNAP in place 25 Rho (ρ) - Independent termination 26 Summary ✤ Transcription makes a copy of the DNA sequence using RNA polymerase and associated proteins ✤ Sequence patterns in DNA and RNA are recognized by proteins, which carry out various roles in transcription ✤ Initiation - RNAP binds to -35/-10 promoter and forms open complex Elongation - synthesis of RNA using DNA template - Rho-dependent or independent dissociation of transcript and RNAP from DNA template 27 ✤ ✤ Termination Ungraded problems ✤ Look over Chapter 12 S1, S2, S3 ✤ Try Chapter 12 C1- C4, C8, C9, C10, C15 28 Next Time Gene regulation in bacteria http://v.mercola.com/ImageServer/public/2007/07--july/7.5milk.jpg 29 ...
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This note was uploaded on 03/29/2009 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas at Austin.

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