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Transcriptional Control

Transcriptional Control. AHMP 5406. Lac Operon. Bacterial example of a genetic switch Operon = group of genes transcribed from a single promoter. Lac Operon. Lac operon controlled by Lac repressor protein CAP Lac operon controls expression of lacZ gene

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Transcriptional Control

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  1. TranscriptionalControl AHMP 5406

  2. Lac Operon • Bacterial example of a genetic switch • Operon = group of genes transcribed from a single promoter

  3. Lac Operon • Lac operon controlled by • Lac repressor protein • CAP • Lac operon controls expression of lacZ gene • Transcription allows bacterium to use lactose

  4. Regulation of Transcription in Euks. • Promoters can be affected by regulatory proteins bound 1000’s of bp’s away • Require several transcription factors • Chromatin packaging can help regulation of transcription

  5. Gene control regions • Control expression of genes • Spread over long stretches of DNA • Promoter • Regulatory sequences • Where regulatory proteins attach

  6. Gene activator proteins • Have 2 domains • One recognizes regulatory sequences • Activation domain – increases rate of transcription initiation • Influence position of RNA polymerase II holoenzyme • Partially assembled • Finished at the promoter

  7. Chromatin remodeling • Can be directed by activator proteins • Recruit remodeling proteins • HATs (histone acetyl transferases) • Histone acetylation increases accessibility • Chromatin remodeling complex

  8. Transcriptional Synergy • Many activators have a greater effect than a single activator

  9. Repressor proteins • Down regulate transcription • Usually do not compete for RNA pol binding sites • Protein-protein interaction

  10. Co-activators/repressors • Do not bind directly onto DNA • Usually too weak to act on their own • Bind to other regulatory proteins

  11. Post Transcriptional Controls • Occur after RNA pol is bound to promoter • Later in pathway • Not as common as previous transcriptional controls

  12. Transcription attenuation • Premature termination of transcription • In bacteria transcript inherently forms 3D structure • Interferes with transcription process • What if the protein is needed? • Regulatory proteins bind to nascent transcript • Stabilize RNA to allow mRNA maturation

  13. Alternative Splicing • RNA can be spliced in several ways • Can make many different proteins from one transcript • Can be tissue specific • Drosophila example • 38K genes from one transcript

  14. RNA editing • Change in mRNA sequence after transcription • Can change reading frame • Indels • Can change codon • Deamination of adenine • Adenosine deaminase acting on RNA enzyme (ADAR) • Produces inosine = A,U, C • C to U • Can make stop codons that truncate protein • Ex. apolipoprotein-B mRNA

  15. mRNA localization • Advantage to have mRNA where protein will be translated • Localization signals • found in 3’UTR • Zip code

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