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Transcriptional repressors ppt Repressor proteins involved in transcription


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DNA & RNA binding repressor proteins

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Transcriptional repressors ppt Repressor proteins involved in transcription

  2. 2. TRANSCRIPTION  Transcription refers to the first step of gene expression where an RNA polymer is created from a DNA template.  Transcription is performed by enzymes called RNA polymerases, which link nucleotides to form an RNA strand (using a DNA strand as a template).  Transcription has three stages: initiation, elongation, and termination.  In eukaryotes, RNA molecules must be processed after transcription: they are spliced and have a 5' cap and poly-A tail put on their ends.  Transcription is controlled separately for each gene in your genome.
  3. 3. REGULATION OF TRANSCRIPTION  Transcription in eukaryotic and prokaryotic cells is controlled by regulatory proteins that bind to specific regulatory sequences and modulate the activity of RNA polymerase.  Thus regulatory proteins and regulatory sequences play a vital role in gene expression.
  4. 4. Regulatory sequences  Any DNA sequence that is responsible for the regulation of gene expression Promoter Enhancer Operator Silencer
  5. 5. Regulatory proteins Any protein that influences the regions of a DNA molecule that are transcribed by RNA polymerase during the process of transcription. Transcription factors Activator Co activator Repressor Co repressor
  6. 6. TRANSCRIPTIONAL REPRESSOR PROTEIN  In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers.  A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.  This blocking of expression is called repression.
  7. 7.  Within the eukaryotic genome are regions of DNA known as silencers.  These DNA sequences bind to repressors to partially or fully repress the expression of a gene.  Silencers can be located several bases upstream or downstream from the actual promoter of the gene.  Repressors can also have two binding sites: one for the silencer region and one for the promoter.  This causes chromosome looping, allowing the promoter region and the silencer region to come to close proximity.
  8. 8. TYPES OF REPRESSOR PROTEINS  Repressor proteins can be DNA- or RNA-binding:  DNA-binding repressors - block the binding of RNA polymerase to the promoter. As a result, the gene is prevented from being transcribed into mRNA  RNA-binding repressors - bind to mRNA, preventing protein translation.  Examples of repressor proteins are lac repressor that inhibits the expression of lac operon in E. coli. Another is MetJ, a methionine repressor of met operon.
  9. 9. EUKARYOTIC TRANSCRIPTIONAL REPRESSORS Passive repressor proteins Active repressor proteins
  10. 10. PASSIVE REPRESSOR PROTEINS:  Passive repressor proteins do not have intrinsic repressing activity or a portable repression domain.  Rather, these proteins repress RNA synthesis by competing with transcriptional activators for DNA binding, by forming inactive heterodimers with transcriptional activators rendering them incapable of interaction with DNA, or by binding to co activators required for the transcriptional activator proteins.  Thus, passive repressor proteins transmit their biological function either via DNA- or protein–protein interactions.
  11. 11.  Inducible cAMP early repressor  bZIP transcription factor family  Sp1-like transcriptional repressors PASSIVE REPRESSOR PROTEINS
  12. 12. ACTIVE TRANSCRIPTIONAL REPRESSORS  Active mammalian transcriptional repressor proteins have an intrinsic repression activity that targets the chromatin organization of the genome.  This type of transcriptional repression is activator-independent and functions over long distances.  Two types of active transcriptional repression can be distinguished:  transcriptional repression via histone deacetylation, and  gene silencing via histone methylation and heterochromatin formation.
  14. 14. CO REPRESSOR  Repressor proteins are influenced by the presence of other molecules, such as co repressors and inducers.  Co repressors are molecules that bind and activate repressors.  Inducers, on the other hand, bind and regulate repressors by inducing the latter to undergo conformational change thereby decreasing binding affinity to the operator.
  15. 15. CO REPRESSOR
  16. 16. TRP OPERON
  17. 17. THANK YOU