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Sites of regulation

Sites of regulation. Feedback inhibition. Mechanism of allosteric inhibition. Repression and Induction. Mechanism of repression- Negative control. Mechanism of repression- control by co-repressor. Operon= a cluster of genes under control of a single promoter Regulon?. Arginine synthesis.

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Sites of regulation

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  1. Sites of regulation

  2. Feedback inhibition

  3. Mechanism of allosteric inhibition

  4. Repression and Induction

  5. Mechanism of repression-Negative control

  6. Mechanism of repression-control by co-repressor Operon= a cluster of genes under control of a single promoter Regulon? Arginine synthesis

  7. Mechanism of induction Lac operon

  8. Mechanism of induction-negative control

  9. Positive vs. Negative control • Repressors are “negative control” • An active repressor (- inducer or + corepressor) stops transcription • Activator proteins are “positive control” • The regulatory protein (activator) promotes transcription • Example: maltose regulon

  10. Activator protein without inducer-positive control

  11. Activator protein with inducer

  12. DNA binding proteins • Non-specific, eg. histones • Small proteins, high + charge • Specific • Frequently dimers • Interact with inverted repeats • Eg. lac repressor

  13. DNA binding proteinsDimeric proteins (e.g., lac repressor) interact with inverted repeats

  14. Attenuation • Positive and negative control affect initiation of transcription • Attenuation affects continuation of transcription • Eg. the tryptophan operon has a leader that includes two tryptophan residues • When tryptophan is lacking, the translation is delayed • The speed of translation determines which of two mRNA double-stranded loops form • One of the two possible loops is a termination signal

  15. How does it work? • Transcription and translation occurring almost simultaneously • Rate of transcription influenced by rate of translation • Translation of leader PEPTIDE regulates transcription • Synthesis of leader terminates transcription, and leader synthesis is inhibited by low Trp

  16. Attenuation: leader sequence

  17. Attenuation: delayed translation Ribosome pauses at trp codon, stem loop that forms DOES not terminate transcription

  18. Attenuation: undelayed translation Leader peptide is formed Stop codon or stem-loop structure can form in mRNA And transcrition is attentuated

  19. Global control: catabolite repression- a variety of unrelated genes regulated Diauxic growth

  20. Catabolite repression • Catabolite activator protein (CAP) assists binding of RNA polymerase to promoter • CAP can bind only when it first binds cAMP • Adenylate cyclase: ATP -> cAMP + pyrophosphate • Glucose inhibits adenylate cyclase and stimulates cAMP excretion • Catabolite repression is similar to positive control, but the difference is the global nature of catabolite repression

  21. CAP binding site on the lac operon

  22. Quorum sensing • Also a form of global control • Relatively recent discovery • AHL-acylated homoserine lactone • Diffusible • Inducer needs activator protein • Example, bioluminescence and luxR activator • Only when [AHL ] is high enough will LuxR activate the lux operon

  23. 2 component regulatory systems • Maltose=effector, BUT if signal not DIRECTLY involved, but needs to be transmitted and changed = signal transduction • Sensor protein= • kinase, phosphorylates compounds, • membrane associated • Phosphoryl group transmitted to another regulator IN the cell • Often a DNA binding protein involved in transcription • Many examples, N-fixation, sporulation,chemotaxis

  24. 2 component regulatory systems

  25. Chemotaxis • Attractants decrease rate of autophosphorylation • Repellant increased autophosphorylation • CheA-CheW=transducer • CheY controls switch • cheY-P tumbles, CCW-CW • CheB phosporylated by CheA-P, but slower response than CheY-P • CheB involved methylation • Fully methylated = best for repellants • cheB-P demethylates, occurs when attractants High • Degree of methylation regulates attraction/repulsion

  26. Chemotaxis

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