Term
| Which enzymes are needed to prepare the mRNA for capping and what do they do? |
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Definition
RNA triphosphate - removes phosphate from the 5' end
RNA guanyltransferase - adds GMP in reverse linkage
RNA methyltransferase - adds a methlgroup to guanosine |
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Term
| How is the cap joined to the 5'end? |
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Definition
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Term
| What is the cap needed for> |
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Definition
Transcription regulation
Promotion of RNA stability and splicing
Export and translation
cell viability |
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Term
| When do capping proteins first bind to RNAP? |
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Definition
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Term
| What (apart from preparing the cap) are methyltransferases and guanyltransferases needed for? |
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Definition
| Relieving the repression caused by DSIF and NELF after proximal pausing |
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Term
| Which major protein complexes bind to the cap? |
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Definition
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Term
| How does CBC bind to the cap? |
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Definition
| The two CBC subunits -cbp80 and cbp20- bind synergistically. cbc 80 causes a conformation change in cbp20 that is required for binding. cbp80 is also the platform for protein recruitment after transcription |
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Term
| What is the CBC a platform for? |
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Definition
| Splicing, transcription, miRNA biogenesis, nonsense mediated decay, pioneer round of translation, mRNA export, mRNA stability, Pre-mRNA 3' end processing |
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Term
| Which enzymes degrade the cap and how? |
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Definition
| Dcp2 hydrolyses the cap , causing mRNA to be rapidly degraded in the 5'-3' direction by exonucleases, and Dcps - hydrolyses cap following degredation from 3'end |
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Term
| Which two proteins bind to emerging RNA molecules and recruit additional proteins to cleave the RNA? |
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Definition
CSTF - cleavage stimulating factor
CPSF - cleavage poladenylation factor |
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Term
| What happens to RNAP after cleavage? |
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Definition
| It continues to transcribe the DNA template, but the merging RNA molecule had no cap and its quickly degraded, causing RNAP to lose its grip on the template DNA |
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Term
| When do CSTF and CPSF bind to the RNA and what does this trigger? |
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Definition
| After the mRNA transcribes the CAP and polyA signals, cleavage |
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Term
| What actually performs the cleavage? |
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Definition
| Within the CPSF complex, CPSF73 is the endonuclease that cleaves pre-mRNA |
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Term
| Which proteins are key to adding the poly-A tail? |
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Definition
Poly-A-polymerase (PAP)
Poly-A-binding protein |
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Term
| What is the poly A signal (PAS) |
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Definition
| A 6 nucleotide AAUAAA signal that triggers cleavage and polyadenylation |
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Term
| What do Downstream sequence elements (DSEs) and Upstream sequence elements (USEs) do? |
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Definition
| Cleavage and polyadenylation specificity factor (CPSF) and cleavage stimulating factor (CSTF) are two multi-polypeptide complexes that, respectively, recognize the PAS and DSEs to promote cleavage between these two elements2,82 |
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Term
| How does the poly A tail enhance translational efficieny? |
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Definition
| By forming a closed loop complex that increases eIF4A and EIF3 recruitment |
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Term
| How does the Poly A tail protect mRNA from degredation? |
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Definition
| it ust be shortened to 10-15 nts before the decapping pathway can begin |
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Term
| What is cytoplasmic polyadenylation? |
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Definition
| Cytoplasmic poly-adenylation is the enhancement of the poly-A tail after an mRNA has exported to the cytoplasm. |
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Term
| How does APA work and what could it be useful for? |
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Definition
In addition to canonical poly(A) site: AAUAAA, nine additional sequences have been identified - these can be used instead.
Could reflect:developmental stage
cellular function
localisation
proliferative status |
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