replication of RNA viruses Flashcards
what are the characteristics of viral RNA dependent RNA polymerase (RdRp)?
act in primer independent way
insensitive for actinomycin D
activity associated with 3Dpol Protein in cytoplasm
replication always takes place at membranes
has right hand pattern
how can RNA viruses be classified?
double strand vs single srand vs ambisense
single stranded can either be + or -
- strands can either be segmented or unsegmented
unsegmented can either be circular or linear
Explain the replication cycle of poliovirus
1.binding to PV receptor capsid opening, RNA release
in cytoplasm
2.polyprotein synthesis
3.Polyprotein processing
in nucleus
4.Pv induced membrane vesicles for transport into nucleus
5.- strand synthesis: Priming reaction at 3’end: VPg is bound to CRE and uridylylated
6. protein transport into vesicles from vesicles to nucleus
7.+ strand synthesis: Vpg is released and uridylylated by 3DPol, Vpg serves as primer
8.packaging and exit
what is the advantage of membrane remodelling during replication of + RNA viruses?
shielding of ds DNA replicative intermediates from inate immune system
resistance against RNases and proteases
high local concentration of viral components
name RNA secundary structures
stem loop: basepairing only in the stem, not within the loop
– kissing loop interaction
– multibranched loop
–interior loop
–hairpin loop
–bulge loop
Pseudoknots: basepairing in the stem and basepairing between loops and external areas
how is the ss +RNA genome structured?
5’ nTR with cloverleaf and IRES (internal ribosome entry side)
CRE (intragenomic cis-active replication element): lies in encoding capacity
3’NTR Pseudoknot
3’ Poly A
How does the cap independent translation in picornavirus work?
inactivation of translation of cellular mRNAs by viral protease that cleave essential eIF4G –> circularisation of cellular mRNA –> host cell shut off!!
cleaved eIF4G binds to IRES of viral RNA –> Translation
Polyprocessing
how is the polioviral genome organised?
Translation of genome into Polyprotein –> hierachy of cleavage
processing done by two viral proteases: 2APro (separates structural and non structural proteins) and 3CPro
temporally and spatially ordered release of functional viral proteins
VPg covalently linked at 5’ end used as protein primer
RdRp not present in particle
genome replication via complementray full-length - strand
how is the picornaviral genome and proteins organised?
VPg Protein at the end used as Primer
encodes for protease, polymerase, membraneanchor and helicase/nTPase and capsid protein
why do RNA viruses code for a single ORF?
Proteolytic cleavage gives rise to equimolar amounts of mature viral proteins
proteolytic cleavage of the polyproteins lead to intermediate and final products which differ in the functions
increase of functional coding capacity
functionally polycistronic, genetically monocistronic
how is the picornavirus replicated?
asymmetrically.
1.- strand synthesis
2.+ strand synthesis
imbalance of + and - strand in infected cell: +>-
CRE loop sequence is template for uridylylation of VPg primers by 3DPol (=covelent linking)
how does the quality control of poliovirus replication work?
1.genome circularisation
2.coordination of translation with genome replication
3.spatial coordination
how does the viral polymerase of poliovirus find its template between all cellular RNAs?
interactions of viral and cellular proteins with RNA secondary structure elements
spatial proximity of synthesized proteins and template RNA in virus induced membrane vesicles (spherula)
why are there more + strands than - strands during the poliovirus RNA replication?
+ strand synthesis is more effective
+ is eventually packed, - is only an intermediate
how is the problem of clashing og replication complex and ribosome in poliovirus solved?
switching between translation and replication
circularisation of genome via protein bridge
switch from translation to replication via local concentration via 3CD –> specific RNA interaction with proteins allows binding of either ribosomes or replication complex
