nidovirales

Question 1

what genome do nidovirales have?

Answer 1

ss + strand RNA genome

Question 2

what is the taxonomy of nidovirales?

Answer 2

Order: Nidovirales
–families: Coronoviridae, Roniviridae, Ateriviridae

Question 3

describe the virus particles of coronoviridae members

Answer 3

-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

Question 4

describe the SARS-CoV-2 infection cycle

Answer 4

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

Question 5

which receptors are used by coronaviruses?

Answer 5

-Mouse Hepatitis Virus: CEACAM1a
-SARS Cov: ACE2
-Hcov-229E: APN

Question 6

what determines host tropoism in coronaviruses infections?

Answer 6

receptor

Question 7

describe the structure of the S-Protein of SARS-CoV-2

Answer 7

-trimer (3 protomers)
-receptor-binding subunit
-membrane fusion subunit

Question 8

what is highly variable between different coronaviruses? What is conserved?

Answer 8

variable: set of accessory proteins
conserved: ORF1a/1b

Question 9

what does the genome of Coronaviruses look like?

Answer 9

-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

Question 10

What does the translation of ORF1a of coronoviruses look like?

Answer 10

translation of ORF1a stops at leaky stop codon –> read through at 25 % of the cases –> -1 frameshift

Question 11

Explain the replication of Coronaviruses

Answer 11

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

Question 12

explain transcription of coronaviruses (altklausur, wichtig)

Answer 12

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

Question 13

explain the translation of coronaviruses

Answer 13

-from each mRNA only the 5’proximal ORF is translated –> functionally monocystronic
-ORF1ab region is processed by virus encoded proteases

Question 14

How many non-structural proteins are encoded in the SRAS-CoV-2 genome? What is their function?

Answer 14

16 non-structural proteins (nsp1-nsp16) –> assemble the replication transcription complex

Question 15

What functions as RNA proofreading in coronaviruses? Which model? What is required?

Answer 15

3’->5’ exonuclease activity of NAsp14 –> backtracking model (trans)

The proofreading requires dimer

Question 16

What is the function of nsp1 in mouse hepatitis virus?

Answer 16

blocking the IFN response of the host

Question 17

what is the function of nsp1 in SARS coronavirus?

Answer 17

-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

Question 18

how is SARS coronavirus mRNA protected from nsp1 activity?

Answer 18

leader sequence in mRNA of virus

Question 19

What can SARS CoV-2 induce in cells? What is needed for that?

Answer 19

Membrane alterations –> pore spanning –> nsp3 and nsp4 are minimal constituents

Question 20

how is SARS cov-1transmitted? When is virus secretion high?

Answer 20

droplet and smear infections –> respiratory and fecal-oral route –> especially high virus secretion in acute phase (fever)

Question 21

what is the incubation time of SARS CoV-1?

Answer 21

4 to 6 (up to 10)

Question 22

what is the mortality of SARS CoV-1?

Answer 22

4-40 %, depending on age

Question 23

How does SARS CoV-1 fulfil Kochs Postulates?

Answer 23

-virus isolated from patients
-cultivation in cell cultures
-experimental infections of macaques (monkey) causes SARS like symptoms
-re-ioslation from diseased animals –> animal model

Question 24

How was SARS-1 stopped?

Answer 24

disruption of chain of infection
-fever controls at borders
-telephone hotlines
-specialized fever clinics
-protection masks
-diagnosis in only 12 h
-quarantine
-effective surveillance

Question 25

Why were the methods to stop SARS-1 effective but is not for example in infleunza viruses or SARS-CoV-2 ?

Answer 25

Onset of symptoms before secretion of infectious virus

Question 26

Can bat coronovarisues infect humans?

Answer 26

A SARS like cluster of circulating bat coronaviruses shows potential for human emergence –> antibodies do not cross-neutralize