Smiley-6: Positive Sense RNA Replication and Expression

Question 1

Most of RNA viruses replicate where?

Answer 1

cytoplasm

Question 2

Do most RNA viruses push host cells into S cells? Why or why not?

Answer 2

• no

- they do not rely on host machinery to replicate

Question 3

What enzyme is used by RNA viruses to transcribe and replicate their genome?

Answer 3

RdRNAP (RNA-dependent RNAP)

Question 4

Are RdRNAP always virally coded?

Answer 4

yes

Question 5

Do +ve sense RNA viruses need to package RdRNAP?

Answer 5

no

Question 6

Why do RNA viruses have very high mutation rates?

Answer 6

RdRNAP lacks proofreading abilities

Question 7

2 differences between RNA and DNA viruses

Answer 7

• all RNA viruses we studied have linear genomes

- RdRNAP does not need a primer to initiate replication

Question 8

2 distinct phases of RNA genome replication

Answer 8

• production of replicative form (RF)

- production of replicative intermediate (RI)

Question 9

Difference between base pairing of RF and RI

Answer 9

RF is ds while RI is not entirely ds

Question 10

subgenomic mRNA

Answer 10

smaller sections of the original transcribed strand

Question 11

poliovirus genome

simple or complex, ss or ds, + or -

Answer 11

simple +ve ssRNA

Question 12

does poliovirus have an envelope?

Answer 12

no

Question 13

What is unique about poliovirus mRNA’s 5’ end?

Answer 13

it does not have a 5’ cap, but it does have a VPg protein covalently linked to it

Question 14

How does poliovirus get its polyA tail?

Answer 14

polyA tail is part of the genome

Question 15

What allows poliovirus to bypass requirement for 5’ cap in translation initiation?

Answer 15

IRES (internal ribosome entry site)

Question 16

How many proteins does poliovirus genome encode?

Answer 16

11

Question 17

What protein(s) cleave the single mRNA transcript into 11 poliovirus proteins?

Answer 17

2A and 3C proteases

Question 18

Where can you find 2A and 3C proteases in poliovirus?

Answer 18

embedded in the polyprotein

Question 19

How are picornaviruses (incl. polio) unusual in its use of one mRNA?

Answer 19

1 mRNA can make all of their proteins

Question 20

How does IRES function to allow translation?

Answer 20

recruits translation initiation factors to RNA –> bound factors recruit ribosomes

Question 21

What must VPg protein linked to in the mRNA genome?

Answer 21

pUpU (diuracyl)

Question 22

How does VPg-UU work to prime synthesis?

Answer 22

U residues anneal to polyA tail of + strand to prime - strand synthesis

Question 23

How does VPg get uridylated (turn into VPg-UU)?

Answer 23

cre in + strand template go into stem loop –> 1st two AA residues serve as template for uridylation of VPg via RdRNAP

Question 24

Does togavirus have an envelope?

Answer 24

yes

Question 25

example of togavirus that we looked at

Answer 25

sindbis

Question 26

How many ORFs does togavirus genome have?

Answer 26

2

Question 27

How does togavirus get its 5’ cap and polyA tail?

Answer 27

they are coded for in the genome

Question 28

How is the togavirus 5’ ORF unusual? (what is it called?)

Answer 28

has an in-frame stop codon that works 75% of the time –> suppressible stop codon

Question 29

How many polyproteins can the 5’ ORF in togavirus actually make?

Answer 29

2 (one short and one long)

Question 30

Which polyprotein in togavirus has the viral RdRNAP?

Answer 30

long polyprotein

Question 31

In terms of P, what is made during early and late polyproteins of togavirus transcription?

Answer 31

• early: P123 +P4

- late: P1 + P2 + P3 + P4

Question 32

What proteins are made from late togavirus polyprotein?

Answer 32

structural polyproteins cleaved to make capsid and envelope proteins

Question 33

describe genome of coronavirus (+ or -, enveloped or not, complex or simple)

Answer 33

complex, +ve ssRNA, enveloped

Question 34

How many ORFs are in coronavirus genome?

Answer 34

5

Question 35

How is coronavirus RdRNAP made?

Answer 35

5’ ORF makes polyprotein that is cleaved to make RdRNAP