repressor

Examples of repressor in the following topics:

• The trp Operon: A Repressor Operon

  • The trp operon is a repressor operon that is either activated or repressed based on the levels of tryptophan in the environment.
  • This operator contains the DNA code to which the repressor protein can bind.
  • When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence.
  • When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.
  • Explain the relationship between structure and function of an operon and the ways in which repressors regulate gene expression

• Transcriptional Enhancers and Repressors

  • Enhancers increase the rate of transcription of genes, while repressors decrease the rate of transcription.
  • Transcriptional repressors can bind to promoter or enhancer regions and block transcription.
  • Like the transcriptional activators, repressors respond to external stimuli to prevent the binding of activating transcription factors.

• Repression of Anabolic Pathways

  • A combination of activators, repressors and rarely enhancers (in prokaryotes) determines whether a gene is transcribed.
  • Another example is when a cell contains a surplus amount of the amino acid tryptophan, the acid binds to a specialized repressor protein (tryptophan repressor) .
  • In bacteria, the lac repressor protein blocks the synthesis of enzymes that digest lactose when there is no lactose to feed on.
  • When lactose is present, it binds to the repressor, causing it to detach from the DNA strand.
  • The repressor is shown in complex with operator DNA (gold) and ONPF (green), an anti-inducer ligand (i.e. a stabilizer of DNA binding).

• RNA Splicing

  • Some of these regulatory proteins include splicing activators (proteins that promote certain splicing sites) and splicing repressors (proteins that reduce the use of certain sites).
  • Some common splicing repressors include: heterogeneous nuclear ribonucleoprotein (hnRNP) and polypyrimidine tract binding protein (PTB).
  • As noted above, splicing is regulated by repressor proteins and activator proteins, which are are also known as trans-acting proteins.

• Slipped-Strand Mispairing

  • If there is a change in the short repeat sequence, it can affect the binding of a regulatory protein, such as an activator or repressor.

• Direct Gene Activation and the Second-Messenger System

  • In the absence of ligand, type II nuclear receptors are often complexed with co-repressor proteins.
  • Ligand binding to the nuclear receptor results in dissociation of the co-repressor and the recruitment of co-activator proteins.

• Initiation of Transcription in Eukaryotes

  • Other proteins known as activators and repressors, along with any associated coactivators or corepressors, are responsible for modulating transcription rate.
  • Activator proteins increase the transcription rate, and repressor proteins decrease the transcription rate.

• Shuttle Vectors and Expression Vectors

  • Please note the presence of a multiple cloning site, a promoter, a repressor, and a selectable marker.

• The lac Operon: An Inducer Operon

  • If lactose is absent, then the repressor binds to the operator to prevent transcription.

• Interferons

  • PI3K activates P70-S6 Kinase 1, an enzyme that increases protein synthesis and cell proliferation; phosphorylates of ribosomal protein s6, which is involved in protein synthesis; and phosphorylates a translational repressor protein called eukaryotic translation-initiation factor 4E-binding protein 1 (EIF4EBP1) in order to deactivate it.