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
Where does N-linked glycosylation occur?
Only in the ER
What is the sugar added to in N-linked glycosylation?
Asn-X-Ser/Thr
How does an N-linked glysoylated sugar get to the Golgi?
Signal is cleaved to only Mannose
Why phosphorylation of Mannose and how?
Transports protein to lysosome
- sugar containing P added to Mannose
- sugar cleaved, giving Mannose-6P
How do mitochondrial proteins get to the matirx
Fully synthesized before entry
- signal sequence helix recognized by OMM receptor
- OMM and IMM line up
- ATP hydrolysis to get protein into matrix
What happens in PDH deficiency
The PDE1alpha subunit cannot be transported into the mitochondria
What are NUPs?
Stand for Nucleoporins, stabilize the nuclear pore
FG NUPs
Form fishing net barrier in pore
- contain transporter receptors
- Phe-Gly repeats
How to nuclear proteins get into nucleus
1) NLS proteins bind cytoplasmic Importins
2) Importins interact with FG-NUP and deliver protein to nuclear cytoplasm
How do proteins get out of nucleus
Exportins
Nuclear Lamina
Thick layer of IF which stabilizes nuclear pores
Progeria
Caused by irreversible Farnesylation of Laminin proteins which stay attached to the Lamina, causing misshapen nuclei and inability to import FG-NUP
- WT has farnesyl group cleaved off
Why is imperfect pairing of miRNA beneficial, and what does it do?
Allows for regulation of related genes
- translational repression
