Transcriptional repressors ppt Repressor proteins involved in transcription

DNA & RNA binding repressor proteins

1. TRANSCRIPTIONAL REPRESSORS T. HEMA MSc BIOCHEMISTRY BHARATHIAR UNIVERSITY 2018-2020

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. 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. Regulatory sequences Any  DNA sequence that is responsible for the  regulation of  gene  expression Promoter Enhancer Operator Silencer

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. 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. 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. 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. EUKARYOTIC TRANSCRIPTIONAL REPRESSORS Passive repressor proteins Active repressor proteins

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. Inducible cAMP early repressor bZIP transcription factor family Sp1-like transcriptional repressors PASSIVE REPRESSOR PROTEINS

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.

13. PROKARYOTIC TRANSCRIPTIONAL REPRESSORS LAC OPERON

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. CO REPRESSOR

16. TRP OPERON

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