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Flashcards in Regulation of Eukaryotic Protein Synthesis Deck (15):

Where can malfunctioning happen for transcription?

1)RNA transcript aborts
2)nonfunctional mRNA sequences
3)retention and degradation in nucleus


Where can malfunctioning happen for translation?

1)translation blocked
2)RNA degraded


How to inhibit protein synthesis specifically eIF2-GDP?

-Double stranded RNA (viral infection)
-Nutrient deprivation
-Lack of heme (can't waste energy on protein synthesis)

^all lead to production of kinase to phosphorylate and inactivate eIF2-GDP and it cannot interact with the exchange factor and no active eIF2-GTP is regenerated (to deliver initiator tRNA)


How do phosphorylated eIF2-GDP inhibit?

It binds eIF2B 100x more avidly
Protein synthesis shits down as all eIF2B is bound in a dead-end complex --> protein synthesis diminishes


Double stranded RNA

Found in life cycle of HCV

DS RNA as an intermediate form --> stimulates shutting down of host protein synthesis

Long double stranded RNA induces production of interferon



Stimulates production of kinase that phosphorylates eIF2-GDP

Phosphorylated eIF2-GDP forms suicide complex with exchange factor eIF2B to inhibit protein synthesis in infected cell



RNA interference can selectively prevent translation and target RNA for degradation



post-transcriptional gene silencing
agent responsible for this is dsRNA

higher eukaryotes: mi RNA (microRNA)


Lower Eukaryotic PTGS

Double stranded RNA mechanism turns off synthesis of certain proteins in a specific manner


Mechanism of RNAi in lower eukaryotes

1) double stranded RNA is cleaved by enzyme Dicer
2) left with 21-25 base double stranded fragments with 2 base overhangs on 3' end
3)Fragments assemble with RISC (silencing complex with endonuclease activity) thru complimentary sequencing
4)siRNA unwinding so that only one strand (anti-sense) stays in the RISC complex
5)Activated RISC
6)RISC associates with target mRNA thru comp sequences
7) Complex cleaved by Slicer
8)Transcription is prevented


Mechanism of RNAi in higher eukaryotes

Do not synthesize long dsRNA
Synthetic siRNA can be introduced to target specific mRNAs for degradation
Then the siRNA is processed same way as lower eukaryotes



Naturally occurring small silencing RNA in mammals

Precursor: Long hairpin structures in the nucleus synthesized by Pol II and processed by Drosha to form pre-miRNA

Transported to the cytoplasm and processed by Dicer--> unwound --> RISC retains antisense strand

miRNA + RISC --> bind to mRNA 3' untranslated regions (imperfect pairing) to inhibit translation (can also lead to mRNA degradation if perfect pairing)

Mediates control of proliferation, cell death, embryonic development, and patterning


How does RISC work in miRNA

1) deadenylation: removes polyA tail on RNA
2)decapping: sequestered in the P body
3) Target mRNA degradation

*no slicing like with siRNA but miRNA binding to 3' untranslated region causes enzymes to remove poly A tail *


Miraversin for HCV treatment

Blocks the actions of Drosha and Dicer for miRNA
Therefore, mature miRNA is never formed from pre-miRNA and then thus HCV RNA will not be made


Gene Therapy

Restore gene where missing/mutant
Suppress expression of mutant/dysregulated gene