L32 Regulation of translation in eukaryotes Flashcards
Eukaryotes vs Prokaryotes
Eukaryotes:
- no RBS
- mRNA recognised by 5’ cap
- mostly monocistronic
- polyA tail
5’ cap
see onenote
Initiation of translation in eukaryotes
see onenote slides
- cap recognition
- scanning by small subunit - kozak
- associaiton of large subunit
- elongation
Leaky scanning
see onenote
can produce alternative proteins
Features of translation in eukaryotes
- physical separation of transcription and translation
- interaction between 5’ cap and polyA tail
5’ cap and 3’ poly A tail interact to form a loop
- Reduce translational efficiency if poly A tail is shortened this is due to the reduction of proximity
- If the association is tight, when the mRNA falls off from the ribosome at the 3’ end, it can be reinitiated at the 5’ more efficiently and quickly as the 5’ end is nearby
IRES
see onenote
cap-independent translation initiation in eukaryotes
very rare
viruses use IRES for translation in host cells
Detecting translatome
see onenote
RNA-seq - what does it tell us?
steady state transcription levels in a cell/tissue
cheap and easy
Translatome - ribosome profiling
see onenote
tells us position of ribosomes on mRNA => which ORFs are being activity translated
Translation efficiency equation
see onenote
Positive = translated efficiently and vice versa
Translational regulation under starvation
see onenote
Regulation of mRNA recognition by TOR kinase
see onenote slides
e1F4F complex required for cap-dependent translation
effect of mTOR inhibition on translation requires 4E-BP
Global vs specific regulation by mTOR
see onenote slides
99% mRNA translationally regulated by mTOR
BUT…SOME mRNA more susceptible to TOR than others:
- Strong enrichment of mRNA associated with translation are down regulated by mTOR
- mRNA with IRES are CAP independent, don’t required recognition of 5’ cap, aren’t down regulated by mTOR
5’ TOP mRNA
5’ TOP mRNAs
- Have 5’ end very rich in C’s and U’s due to association of 4E-BP binding protein to 5’ region of mRNA, better affinity for 4E-BP. If the sequence has higher affinity for 4E binding protein, would be more sensitive to mTOR regulation
- If they have TOP mRNA, strong skew of regulation by mTOR
mRNA-specific translational repression by 4E-BP
see onenote
polar nucleolisation of mRNAs in Drosophila oocyte
- During trafficking process, need repression of translation of that mRNA
mRNA-specific translational repression by 4E-BP - Oskar
see onenote
posterior localisation of maternal oskar mRNA establishes polarity in Drosophila oocyte
How is translation of Oskar mRNA repressed during transport?
see onenote
mRNA-specific translational repression by a cup, 4E-BP
abundance of cup is too low to repress all mRNA, Bruno required to recruit Cup to Oskar mRNA
Iron homeostasis - balancing deficiency and excess
Ferritin vs Transferrin
see onenote
Ferritin - iron storage protein: buffers against toxicity and deficiency, less ferritin produced when there is lack of Fe
Transferrin receptor is an Fe uptake protein, required for Fe uptake under low Fe conditions (opposite to ferritin)
Aconitase in a cytosolic Fe-containing enzyme
Sufficient iron in cell:
IRP1 = aconitase, Fe containing enzyme
Insufficient:
Fe-free aconitase becomes an RNA binding protein
- Aconitase has dual function
- IRP1 acts as aconitase, binds to iron when there’s too much iron
- IRP1 becomes an RNA binding protein when there isn’t enough iron. Binds to IRE (iron regulatory element).
Regulation of translation initiation by IREs - starvation vs excess
see onenote slides
IRE = secondary structure in mRNA
Regulation of mRNA stability by IREs
see onenote
IREs present in 3’ UTR of transferrin receptor mRNA
IREs can have opposite effects on post-transcriptional regulation
Translational control by miRNAs
see onenote slides
miRNAs contribute to translational repression but mechanism not well defined
RISC complex
- Repress translational initiation, reduce translation efficiency
- Interferes with close-looped structure
- GW182 interacts with polyA binding protein, disrupts close-looped structure => reduced translation efficiency
