Lecture 16 (-)ssRNA viruses

Rhabdoviruses & Orthomyxoviruses; for the final

T/F: (-)ssRNA genomes are translatable

False

What is (-)RNA complementary to?

mRNA/(+)RNA

What is viral ss(-)RNA transcribed into?

(+)mRNA or sense mRNA

T/F: Genome RNA alone is infectious

False

What is the polymerase for (-)ssRNA viruses?

RNA-dependent RNA polymerase (RdRp)

T/F: All (-)ssRNA viruses are enveloped

True

What are the major nonsegmented (-)ssRNA families?

1) Rhabdoviridae

2) Paramyxoviridae

3) Filoviridae

Characteristics of Rhabdovirus virions

Bullet-shaped

Envelope has spike proteins

~11-15 kB

Helical capsid

RNA wrapped w/ N protein

What is the shape of Rhaboviruses?

Enveloped helical

Hosts of Rhabdoviruses

Diverse

Vertebrates, invertebrates, plants

Mammals, fish

What is (-)ssRNA genomes usually wrapped with?

Viral protein N

What notable virus is in the Rhabdoviridae family?

Rabies virus

Rabies virus

Infection via saliva

Wide host range

Causes fatal encephalitis

T/F: After someone is exposed to rabies, they can’t be vaccinated for it

False

VSV-G

Glycoprotein of Vesicular stomatitis virus

Infects membrane in the mouth

Used as a pseudotype

Why is VSV-G widely used to pseudotype various viral expression vectors?

1) Can infect almost any type of cells

2) Very sensitive to interferons

3) Exceptional virion model

What are the major Rhabdovirus proteins packaged in the virions?

1) N

2) P

3) M

4) G

5) L

N protein

Nucleoprotein in rhabdoviruses

Forms the helical nucleocapsid

Wraps the genome’s RNA

P protein

Phosphoprotein in rhabdoviruses

Associated w/ the N protein

L protein

Large proteins in rhabdoviruses

Associated w/ N proteins

Multifunctional: RdRp, capping, poly(A), and kinase activities

M protein

Matrix protein in rhabdoviruses

Forms layer b/w nucleocapsid & envelope

Inhibits transcription

G protein

Glycoprotein in rhabdoviruses

Form the spikes in the envelope

How does the M protein inhibit transcription?

1) Via all 3 host RNA polymerases

2) Blocks intracelluar transport of cell RNAs & proteins

What is unique about plant Rhabdoviruses?

They replicate in host vector AND in plant hosts

Can RdRp or its activity be found in mature Rhabdovirus virons?

Yes; it is seen in the L proteins

What does the rhabdovirus L protein encode for?

1) RdRp

2) Capping

3) Polyadenylation (PolyA tail0

4) Kinase activities

Do rhabdoviruses need a primer for replication?

No

T/F: (-)ssRNA viruses do NOT need a primer for replication

True

T/F: (-)ssRNA viruses have a 5’ cap

False

Describe the cap of Rhabdoviruses

They don’t have one

Why don’t (-)ssRNA viruses have a 5’ cap or 3’ poly-A tail?

Negative/antisense RNA genomes don’t have them

They need viral enzymes to make them within the host cells so they can be translated

Where do Influenza viruses replicate?

Nucleus

What important virus is in the Orthomyxoviridae family?

Influenza virus

Diseases caused by Paramyxoviruses

Measles

Respiratory syncytial viruses (RSV)

Nipah & Hendra

Measles virus

Contagious

Cause immunosuppression that eliminates immune memory

Can be prevented by MMR vaccine

(-)ssRNA viruses w/ segmented genomes

1) Orthomyxoviridae

Structure of Orthomyxoviruses

Linear (-)ssRNA

6-8 segments that are individually wrapped in helical nucleocapsids

Enclosed in lipid envelope

Where do Orthomyxoviruses get their envelopes from?

Host cell’s plasma membrane

How many segments are in Influenza viruses?

8

How many different viral proteins are there in Influenza viruses?

11

T/F: All 11 Influenza viral proteins are packaged into viral particles

False

What are some of the major viral proteins in Influenza viruses?

1) HA

2) NA

3) M2

4) M1

5) Three RNA Pol proteins (PA, B1, PB2)

6) NS1

What are the 3 components of RdRp in Influenza viruses?

1) PA

2) PB1

3) PB2

HA protein

Hemagglutinin in Influenza

Envelope glycoprotein

Responsible for fusion

Binds to sialic acid/cell receptors

NA protein

Neuraminidase in Influenza

Releases the virus

Cleaves sialic acid

Target of Tamiflu

What must happen to activate Influenza virus?

Cellular proteases cleaving HA

Need to expose the fusion peptide

M1

Matrix protein in Influenza viruses

Helps link spike protein to viral core

M2

Ion channel on Influenza envelope

Blocked by Amantadine

NP

Nucleocapsid protein in Influenza

NS1

Nonstructural protein 1 in Influenza viruses

Suppresses cell’s antiviral responses

Cap snatching/stealing

Influenza virus steeals 5’ cap from cell’s mRNAs

Inhibiting this is an effective antiviral measure

T/F: Influenza virus requires a primer

False

Steps of Influenza virus replication

1) NP enters the nucleus

2) Does NOT need a primer

3) NO 5’ cap, 5’ ppp cap instead

Antigenic drift

Slow, continuous amino acid changes/mutations

Cause changes in antigenic structures over time

Antigenic shift

Major change in HA or NA subtype

Results from a reassortment during a mixed infection w/ 2 or more subtypes

Why do we have seasonal Flus?

Antigenic drift → yearly virus changes and environmental factors like colder weather helps the virus spread

Why do we have pandemic Flus?

Antigenic shifts → Humans don’t have complete immunity to animals, which causes widespread global outbreaks

Genome assortment

How genetic material is shuffled/distributed

Mendel’s Law of Independent Assortment

Genes sort independently of each other during gamete formation