Quiz 4 Flashcards
VPg not involved in
Translation
40S subunits binds to
- ribosome landing pad
- completely bypass 5’ end
- analogous to Shine-Delgarno sequence
Single ORF encodes
polyprotein - beads on a string
Polyprotein Processing Step 1
- Ribosome binds to RLP and translation occurs
- P1-2A polyprotein fragment created
- Protease 2A cleaves P1 co-translationally. reaches around and cleaves its own N terminus
- Free P1 and 2A is still there
Polyprotein Processing Step 2
- Translation of P2-3ABC
- Protease 3C protease cleaves co-translationally to release P2
Polyprotein Processing Step 3
- Translation of P3
- Protease 3C post-translationally cleaves P1, P2, and P3
VP0 cut by
- not cut by any of the viral proteases
- cleaved autocatalytically inside assembled provisions
Cleaves co-translationally
-Protease 2A and 3C
Cleaves post-translationally
-Protease 3C only
Replicase
- composed of viral RdRp plus other host cell proteins needed for replication
- bound on membrane on cytoplasmic side
5’ caps on ssRNA virus
added post transcriptionally by virus encoded enzymes in the cytoplasm
poly A tails on ssRNA
generated by template copying (copying a poly U)
vpg on ssRNA
- what you start with (“primer”)
- first nucleotide joins to the vpg
- not added as a post-transcription mechanism
How to choose - strand more than + strand
- adjust how well the enzymes bind
- tight binding on 3’ end of - strand to make new + strands
Why don’t + strand RNA molecules get spliced?
- they are found in the host cytoplasm and never come into contact with host cell splicing machinery.
Advantages of transient dsRNA
- all unwound at the end - good
- 3’ end exposed. Binding site exposed so replicase can bind and make negative sense and now the binding site on the 3’ of negative site has high affinity
has multiple replication sites so have different convoys(all making the same amount of time so you make more) of RNA running down the (-)-RNA, bc you want a highly translated RNA. 3’ end is unwound so they won’t run into to each other.
P3 protein
- used for genome replication but must have beads attached
what determines rate of initiation of RNA synthesis?
- steady-state concentration of P3
If P3 is cleaved before it binds to RNA
it can’t function in replication
After P3 binds to RNA
cleavage must occur prior to elongation phase of RNA synthesis because the 3D (RNA poly) is tethered to the P3.
Poliovirus RNA synthesis initiation
- P3 binds to 3’ end of viral RNA template
- 3D copies template and joins first nucleotide to Vpg
- 3D poly joins second nucleotide to first
- 3D poly stalls because it is still tethered to P3 and must be cleaves to move on.
Poliovirus RNA synthesis elongation and termination
- 3C protease cleaves P3 and 3D moves on
- Untethered 3D along, elongating, until it reaches 5’ end of template and detaches.
the mechanism for poliovirus assembly and maturation
nucleation mechanism
Once all 12 pentamers are bound together
provirion
Early and late stages of infection cycle
Early - plus strands all go into making new minus strands.
Later - instead of genome replication and gene expression it goes into assembly.
Togavirus
- has an envelope
- RNA looks just like a cellular message.
Two genera of Togavirus
- alphavirus
- rubivirus
Alphavirus
- transmitted by arthropods
- New World (Americas) and Old World (Everywhere else)
- animal and insect reservoirs
- encephalitis, polyarthritis, and/or rash
- no vaccines for humans
Rubella Virus
- infects only humans
- respiratory-aerosol (droplet) and placental-fetal transmission
- infection of developing fetus (congenital rubella syndrome)
- controlled by vaccine
