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Generalities for Transcriptional Regulation

Generalities for Transcriptional Regulation. Activators and Repressors Act in Concert Effector Binding Changes Protein Shape DNA Binding Occurs at Specific Sequences DNA Looping Common Feature. Eukaryotes vs. Prokaryotes. Complexity of Genome Multiple, Compartmentalized Chromosomes

pandora-cummings
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Generalities for Transcriptional Regulation

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  1. Generalities for Transcriptional Regulation • Activators and Repressors Act in Concert • Effector Binding Changes Protein Shape • DNA Binding Occurs at Specific Sequences • DNA Looping Common Feature

  2. Eukaryotes vs. Prokaryotes • Complexity of Genome • Multiple, Compartmentalized Chromosomes • Transcription Separated from Translation • Transcript Processing • Multi-Cellular

  3. Transcriptional Regulation Translational Regulation

  4. Eukaryotic RNA Polymerases • RNA Polymerase I • Ribosomal RNA Genes • RNA Polymerase II • Protein Coding Genes • RNA Polymerase III • Transfer RNA Genes

  5. Hsp 83 RNA Accumulation During Drosophila Embryogenesis

  6. Enhancerscis-acting elements • Act at a distance • May be upstream or downstream • Bind Activators and/or Repressors • Can act on additional genes

  7. Fig. 16.5

  8. lacZ gene Hsp83-lacZ Reporter Construct

  9. Enhancer lacZ expression Pattern -873.+1621 -873.+1009

  10. Activating Transcription Factors • Great Diversity • Protein Domains • DNA Binding Domain • Activator Domain • DNA Binding Domain Motifs • Helix-Turn-Helix (aka. Homeodomain) • Zinc Finger • Basic Leucine Zipper • Helix-Loop-Helix

  11. Homeodomain (Helix-Turn-Helix)

  12. Zinc Fingers

  13. Steroid--Steroid Receptor Complex Receptor Hormone

  14. Basic Leucine Zipper (bZIP) Fig. 16.7

  15. Activator Repressor Myc/Max Helix Loop Helix Fig. 16.10

  16. Fig. 16.8

  17. Fig. 16.11

  18. Chromatin Structure and Gene Expression • Dampens Transcription to Low Levels • Major Means of Keeping Expression Turned Off • In contrast, prokaryotes utilize repressors • Chromatin remodeling precedes activation • Reflected by DNAase I hypersensitivity • Heterochromatin Silences All Transcription • Example: X-inactivation and formation of Barr Bodies

  19. Sex Determination in Drosophila • XX Females, XY Males • Early Embryo “Counts” the X Chromosomes • Sex Lethal (Sxl) Gene Critical Regulator • Mutations in Sxl Result in NO Females! • Sex Lethal Acts at the Level of Splicing • RNA-Binding Splice Factor

  20. Females (XX) Males (XY) Early Embryo Helix-Loop-Helix Homodimers NO Helix-Loop-Helix Homodimers Fig. 16.16

  21. Females (XX) Males (XY) Splicing Occurs at start of Exon 2 Splicing Occurs within Exon 2 mRNA lacks premature stop codon; transformer protein functional Sex lethal regulation of transformer RNA splicing Sex Lethal Protein No Sex Lethal Protein Stop codon mRNA include a premature stop codon; transformer protein nonfunctional after Fig. 16.16

  22. Regulation of Gene Expression via RNA Stability RNA in situ Northern Blot

  23. Mechanisms to Degrade mRNA • Poly-A Tail Length • Long tails confer stability • Tail shortening leads to mRNA turnover • Degradation Sequences • Map to 3’ (or 5’) Untranslated Regions • Interact with protein factors that degrade the “targeted” mRNA

  24. Reporter Constructs Are Used to Identify Degradation Sequences

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