Offner Regulation of Protein Synthesis Flashcards
Mechanism of Global inhibition of translation
1) Virus produces dsRNA stimulating kinase production
2) Kinase phosphorylates eIF2-GDP
3) eIF2-GDP forms suicide complex with eIF2B
4) protein synthesis inhibited by lack of eIF2
RNAi
lower eukaryotes
1) Dicer cleaves dsRNA into multiple siRNA
2) RISC binds and unwinds siRNA
3) Holds onto antisense RNA strand
4) RISC binds target mRNA
5) Argonaute enzyme (slicer) within RISC causes mRNA degradation
Argonaute enzyme (Slicer) only works in a very specific case. What is it?
The antisense RNA strand has to be perfectly paired with the target mRNA
miRNA
Higher eukaryotes
1) long hairpin miRNA precursors synthesized by Pol II
2) processed by Drosha to form pre-miRNA
3) pre-miRNA transported to cytoplasm and processed by Dicer
4) Argonaute (RISC) unravels and selects ssRNA
4) RISC binds to mRNA 3’ UTR to inhibit translation
Can miRNA regulate gene expression? What percentage?
Yes, 20-30%
Does miRNA require perfect pairing?
No
Perfect pairing
cleavage of target mRNA by Slicer
What do cytoplasmic ribosomes produce?
Cytoplasmic, mitochondrial and nuclear proteins
What do ER bound ribosomes produce?
Membrane, secretory and lysosomal proteins
Localization signal for mitochondrial proteins
30-50aa presequence at 5’ end with amphipathic character
Where would a 20-30 amino acid “signal sequence” with a core of hydrophobic amino acids target proteins?
Membrane and secretory locations
Where would Mannose-6P target a protein?
Lysosome
Mechanism of co-translation insertion into the ER membrane
1) SRP binds and interrupts translation
2) SRP binds receptor in ER membrane and threads membrane through
3) SRP and SRPR leave, translation re-initiated
If co-translationally produced protein is secretory what happens, and what enzyme is used?
hydrophobic signal region is cleaved by signal peptidase
What type of protein is produced in stop-transfer fashion?
Membrane targeted proteins, stop-transfer leads to creation of a transmembrane region
