Lecture 14 Reoviruses

For the final

Where do dsRNA viruses replicate?

Cytoplasm

Can dsRNA viruses be directly translated?

No

Structure of reoviruses

Spherical, icosahedral symmetry

Hosts for reoviruses

Very broad

Mammals, birds, plants, fish, fungi

Genome of reoviruses

dsRNA

What’s the main disease caused by reovirus infection?

Gastroenteritis

Which enzymes are in the rotavirus core?

VP1 and VP3

Role of VP1 in rotaviruses

Making RNA-dependent RNA pol

Role of VP3 in rotaviruses

Making guanylyl transferase and methyl transferase for capping

Families of reoviruses

1) Orthoreoviruses

2) Rotaviruses

Are VP1 and VP3 structural proteins?

Yes. Polymerases and enzymes are considered structural proteins

How many dsRNA segments are in rotaviruses?

11

Viroplasm

Discrete regions in the cytoplasm where virus proteins gather

In rotaviruses, what happens in the viroplasm?

VP1, VP2, and VP3 assemble virion cores

How many copies of VP1 and VP3 are in rotaviruses, and where are they?

12 copies; each are vertices of the icosahedral structure

Methods for rotavirus entry

1) Direct penetration

2) Endocytosis

Describe direct penetration in rotaviruses

Controlled by hydrophobic region of VP5

Allows uncleaved spike proteins to enter

Describe endocytosis in rotavirus

Clathrin relies on the B1 integrin

What happens to rotaviruses when they enter endosomes?

1) Outer capsid is stripped from virions

2) Core is released into cytoplasm

What is the mode of replication in rotaviruses?

Conservative

What does VP1 synthesize in rotaviruses during entry?

1) A new (+)RNA genome using (-)RNA

2) A molecule of VP3 that caps the new (+)RNA

True or false: All segments of (+)RNA rotavirus genome are made at the same time

True

True or false: Newly made rotavirus (+)RNA have a polyA tail

False

Which proteins form viroplasms?

NSP2 and NSP5

What does (+)RNA give to rotavirus cores upon entry?

1 each of 11 RNA species

Infectious subvirion particles (ISVPs)

Rotavirus virions partially degraded by cathepsins

Allows cell to become infectious

What happens when creating ISVPs in rotaviruses?

1) Outer layer (VP7) is lost, making a double-layered particles

2) VP4 cleaves into VP8 and VP5

3) Allows cell to start copying RNAs

Where does transcription occur in rotaviruses?

In the double-layered particles

List the steps of late rotavirus transcription & translation

Late transcription → late mRNA → viral protein synthesis

What do VP1/RdRps make during rotavirus transcription?

Late uncapped transcripts

What happens during rotavirus translation?

Cell protein translation shuts down while virus translation continues

What is the cap of an early rotavirus transcript?

VP3 adds a 7-methylguanosine 5’ cap

What is the cap of a late rotavirus transcript?

There is none

What is the polyA tail of a rotavirus?

There are none; rotaviruses have no polyA tail at the 3’ end

List the proteins for each layer of a rotavirus capsid

1) Inner= VP2

2) Middle= VP6; contains wheel’s “spokes”

3) Outer= glycosylated VP7 from membrane ER

Inner protein

VP2

Middle protein

VP6

Outer protein

Glycosylated VP7