Control of Translation

Question 1

In HCV ____ is recognized by the 40S subunit/eIF3 complex

Answer 1

IRES

Question 2

How does the new drug Ataluren possibly cure CF?

Answer 2

In a CF variant with a single point mutation causing an early stop codon, Ataluren interferes and facilitates complete translation

Question 3

In the initiation of eukaryotic protein synthesis, what does eIF-2-GTP do?

Answer 3

Binds the initiator tRNA and forms a complex with the 40S r subunit

Question 4

How is eIF-2-GTP rejuvenated (from GDP) after it contributes to initiation?

Answer 4

A guanine nucleotide exchange factor, eIF2B

Question 5

What cellular conditions lead cells to limit protein synthesis?

Answer 5

ds RNA (virus presence)
Stress
Nutrient deprivation
Lack of heme

Question 6

When cells wish to inhibit synthesis, how is eIF2 affected?

Answer 6

A kinase phosphorylates eIF2B (the exchange factor), very tightly, thereby shutting down protein synthesis

Question 7

What anti-viral agent is stimulated by presence of ds RNA and what follows?

Answer 7

Interferon…upregulates kinase that phosphorylates eIF2-GDP (shuts down protein synthesis)

The cell wants to STOP the virus from being able to make protein

Question 8

What is the primary mechanism of post-transcriptional gene silencing in lower eukaryotes? in upper?

Answer 8

Lower euk = dsRNA

Higher euk = microRNAs (miRNAs)

Question 9

What happens when lower eukaryotes detect long strands of dsRNA?

Answer 9

An enzyme, DICER, will cleave the long strands of ds RNA and the little pieces will bind to RISC (RNA-induced silencing complex). An enzyme within RISC called Slicer will degrade the mRNA.

Question 10

What are the differences in siRNA processing in higher eukaryotes?

Answer 10

Higher eukaryotes do not have DICER, but the rest is the same

Question 11

What are miRNAs?

Answer 11

Naturally occuring silencing RNAs in mammalian cells

Synthesized as longer hairpin precursors in the nucleus by Pol II processed by Drosha to form pre-miRNA

Question 12

What are two key difference between miRNA and siRNA

Answer 12

1. miRNA targets are almost always in the 3’ untranslated region and pairing need NOT be perfect.

In contrast, siRNA targets are usually in the coding region and pairing is perfect.

2. Ultimate goal is usually inhibition of translation

Question 13

How does pre-miRNA become mature miRNA?

Answer 13

Pre-miRNA (hairpin ds microRNA) is cleaved by DICER

Question 14

During miRNA processing, the _____ strand stays and the _____ strand is removed.

Answer 14

Antisense strand stays, sense strand removed

Question 15

If miRNAs have imperfect pairing they will work via _________. If perfect pairing, they will work via ________.

Answer 15

Imperfect: translational repression

Perfect: cleavage of target mRNA by Slicer

Question 16

Because miRNA do not require perfect pairing, they can bind ______ different regions.

Answer 16

multiple

Question 17

When RISC binds the untranslated region, what is the first thing that happens?

Answer 17

A bunch of enzymes de-adenylate the polyA tail, sequestering the mRNA. This is followed by cap removal and targeted mRNA degradation