nidovirales Flashcards
what genome do nidovirales have?
ss + strand RNA genome
what is the taxonomy of nidovirales?
Order: Nidovirales
–families: Coronoviridae, Roniviridae, Ateriviridae
describe the virus particles of coronoviridae members
-lipid envelope with proteins: S Protein (spike for receptor binding and membrane fusion), HE (hemagglutinin-Acetyl Esterase), E (small envelope protein for budding), M (membrane for contact toi nucleocapsid)
-nucleocapsid: Genome and N - Protein
-no ikosehadral internal structure of the virion
describe the SARS-CoV-2 infection cycle
1.viral entry via membrane fusion with viral entry via endocytosis
2.translation of ORF1a and ORF1b
3.Polyprotein processing
4.Formation of replication organelles
5.replication of gRNA and transcription of sg-mRNA
6.Translation of structural and accessory proteins
7.assembly of nucleocpasid
8.Formation of virion: virion maturation, spike cleavage
9.excocytosis
which receptors are used by coronaviruses?
-Mouse Hepatitis Virus: CEACAM1a
-SARS Cov: ACE2
-Hcov-229E: APN
what determines host tropoism in coronaviruses infections?
receptor
describe the structure of the S-Protein of SARS-CoV-2
-trimer (3 protomers)
-receptor-binding subunit
-membrane fusion subunit
what is highly variable between different coronaviruses? What is conserved?
variable: set of accessory proteins
conserved: ORF1a/1b
what does the genome of Coronaviruses look like?
-RNA genome (ss +)
-5’ UTR with cap
-9-14 ORFS (ORF1 followed by structural proteins He, S,E,M,N and acessory proteins)
-3’UTR with poly A
ORF1 encodes a polyprotein which proteolytically processed into replicase subunits nsp1-16
What does the translation of ORF1a of coronoviruses look like?
translation of ORF1a stops at leaky stop codon –> read through at 25 % of the cases –> -1 frameshift
Explain the replication of Coronaviruses
1.translation of incoming genome
2.assembly of replicase
3.synthesis of complete - strand which is complementary to + strand
4.synthesis of many + strand genomes on- strand template
explain transcription of coronaviruses (altklausur, wichtig)
one single negative strand RNA serves as a template for synthesis of many mRNA molecules
The genome has several TRS
–>special mechanism: discontinous transcription (leader primed):
-negative strand Synthesis Starts at 3’ end of genome
-RdRp stops at internal genomic sequence (TRS = transcription regulating sequence) of - strand
–> base pairing between TRS of - strand and leader TRS of + genome strand RNA (=template)
-Transfer of this short, just generated -strand to the TRS at the 3’ end of the +strand
-restart of RNA synthesis and completion of - strand synthesis (5’ends of all negative strands identical = each RNA includes leader sequence)
-these negative strands are then called subgenomic RNA
-subgenomic negative strand RNA serves as template for synthesis of mRNA
-capping by viral enzymes
–>a nested set of 3’ co-terminal mRNAs with identical 5’ sequence is generated
explain the translation of coronaviruses
-from each mRNA only the 5’proximal ORF is translated –> functionally monocystronic
-ORF1ab region is processed by virus encoded proteases
How many non-structural proteins are encoded in the SRAS-CoV-2 genome? What is their function?
16 non-structural proteins (nsp1-nsp16) –> assemble the replication transcription complex
What functions as RNA proofreading in coronaviruses? Which model? What is required?
3’->5’ exonuclease activity of NAsp14 –> backtracking model (trans)
The proofreading requires dimer
What is the function of nsp1 in mouse hepatitis virus?
blocking the IFN response of the host
what is the function of nsp1 in SARS coronavirus?
-binds to 40S ribosomal subunit
-stops translation of cellular mRNA
-modifies 5’end of mRNA to render it translationally incompetent
-induces endonucleatic cleavage of mRNA near the 5’ end
how is SARS coronavirus mRNA protected from nsp1 activity?
leader sequence in mRNA of virus
What can SARS CoV-2 induce in cells? What is needed for that?
Membrane alterations –> pore spanning –> nsp3 and nsp4 are minimal constituents
how is SARS cov-1transmitted? When is virus secretion high?
droplet and smear infections –> respiratory and fecal-oral route –> especially high virus secretion in acute phase (fever)
what is the incubation time of SARS CoV-1?
4 to 6 (up to 10)
what is the mortality of SARS CoV-1?
4-40 %, depending on age
How does SARS CoV-1 fulfil Kochs Postulates?
-virus isolated from patients
-cultivation in cell cultures
-experimental infections of macaques (monkey) causes SARS like symptoms
-re-ioslation from diseased animals –> animal model
How was SARS-1 stopped?
disruption of chain of infection
-fever controls at borders
-telephone hotlines
-specialized fever clinics
-protection masks
-diagnosis in only 12 h
-quarantine
-effective surveillance
Why were the methods to stop SARS-1 effective but is not for example in infleunza viruses or SARS-CoV-2 ?
Onset of symptoms before secretion of infectious virus
Can bat coronovarisues infect humans?
A SARS like cluster of circulating bat coronaviruses shows potential for human emergence –> antibodies do not cross-neutralize
