Lecture 15 Picornaviruses

For the final

What diseases are caused by picornaviruses?

Common cold

Poliomyelitis (Polio)

Hepatitis A

Foot and Mouth disease

What is the cell receptor for poliovirus?

CD155 or PVR

Aka canyons

What is the virion structure of picornaviruses?

Naked icosahedral capsid

True or false: picornavirus genome can be directly translated

True

Can poliovirus genomic RNA alone be used to initiate viral infection?

Yes, as long as it’s delivered into the host cell

In picornaviruses, is a 5’ end cap required to act as mRNA for protein translation?

No

Why isn’t a 5’ end cap required to act as mRNA for protein translation?

Picornaviruses have IRES at the 5’ end, which allow translation to happen without a cap structure

Which viral protein is released when poliovirus binds to the cell receptors?

VP4

Genome of picornaviruses

Linear (+)ssRNA

Do picornaviruses always carry their replicase inside mature viral particles?

No, since they produce replicase after gaining cell entry

What is the replicase in picornaviruses?

RNA-dependent RNA polymerase (RdRp)

True or false: Translation occurs after transcription in Class IV (+)ssRNA viruses

False

Where does RNA replication take place in Class IV (+)ssRNA viruses?

On membranes

What is one unique feature of picornaviruses regarding transcription and translation?

They happen at the same time because of IRES

Internal Ribosome Entry Sites (IRES)

Allow ribosomes to directly bind to the viral RNA’s 5’ end

Bypasses normal capping

Initiates translation internally

What are the purposes/functions of (+)ssRNA in Class IV (+)ssRNA viruses?

1) Templates for (-)RNA synthesis

2) Act as mRNA

3) Progeny virion genomes

What are the major translation strategies used by Class IV (+)ssRNA viruses?

1) Polyproteins

2) Subgenomic mRNAs

3) Segmented genomes

Polyproteins

All genetic information is encoded in 1 ORF & translated into this

Eventually cleaved to produce individual virus proteins

ORFs

Opening reading frames

Continuous stretch of DNA/RNA w/ start and end codons

Subgenomic mRNAs

Genome has 2 or more ORFs

RdRp encoded by ORF at 5’ end

Other ORFs have same 3’ end as the rest of the genome

Segmented genome

There is 1 ORF in each RNA segment

Which viral protein is bound to the 5’ end of the picornavirus genome?

VPg (22aa)

T/F: Picornavirus (+)ssRNA genome has a poly A tail

True

What is/are the first molecule(s) synthesized after a picornavirus infection?

Viral proteins

T/F: There is no Hepatitis A vaccine

False

T/F: Improved hygeine reduces risk of polio

False

What was the first virus to have an inactivated vaccine?

Poliovirus

Rhinoviruses

Cause common colds

How is the translation of pre-existing cell mRNAs inhibited?

Viral protease 2A cleaves translation initiation factor elF4G

How is VPg used as a primer for viral genome replication?

1) Poliovirus RNA Pol uridylyates VPg at OH- group of tyrosine residue

2) Primese synthesis of BOTH (+) and (-) viral RNA strands

T/F: In picornaviruses, only (+)ssRNA is made during genome replication

False

T/F: CD155/PVR is a glycoprotein

True