dsRNA Flashcards
What are class three viruses
dsRNA
ALL have segmented genome
What are examples of dsRNA viruses
Reovirus
Rotavirus
Blue tongue virus
What are the basic morphological features of rotavirus?
dsRNA, total 18.5 kB genome size
non-enveloped, 75nm
icosahedral capsid with helical dsRNA
genome is surrounded by a three layer icosahedral capsid
11 segments of helical dsRNA
segments 1-10 code for one protein
segment 11 code for two proteins
each particle contains ONLY ONE copy for each segment
Where does transcription and replication occur for Rotavirus
occurs in the CYTOPLASM
What is the route of transmission for Rotavirus and where does the infection spread
fecal-oral route
infects cells of the small intestine
What is the impact of rotaviruses on humans, is there a vaccine
can cause severe gastrointestinal disease in humans
most common cause of diarrhea in children worldwide
adults are rarely affected
causes about 200,000 deaths a year, mainly in third world countries due to contaminated water, it spreads oral-fecal route
there is a vaccine available, prior to the vaccine there was 60000 hospitalizations in the united states
How do dsRNA viruses replicate
conservatively
they use the + strand RNA (mRNA) as a template
Can dsRNA function as mRNA?
no,
the parent strand must separate
or
transcription of + strand RNA from - strand RNA
Where is RNA transcribed and how is this process activated
Rotavirus RdRP (RNA dependent RNA polymerase) is part of the viral particle and is active when the proteins in the particle are degraded during uncoating and it produces mRNA molecules through pores of the external spikes
in the cytoplasm of the host cell
inside the core particles of the virion
during uncoating the virion loses some structural proteins but a core of capsid proteins remain
mRNA leaves through the channels of the spike protein
Why can’t a viral genome be transcribed inside of the virion?
can’t translate inside the core of the virion because viruses do not have ribosomes, they have to use host ribosomes
Do Rotaviruses contain a 5’ cap or polyA tail on mRNA?
Rotaviruses contain a 5’ cap on mRNA but do NOT have a polyA tail
What makes up for the missing polyA tail on mRNA in Rotaviruses
NSP3 acts as a translational enhancer to make up for the lack of polyA tail
What is the role of NSP3 in Rotaviruses
NSP3 acts as a translational enhancer to make up for the lack of polyA tail
NSP3 is the viral replacement of PABP which is on human mRNA
binds to the 3’ end of genome and eIF4G
NSP3 has a stronger binding to eIF4G than PABP (in cellular mRNA), therefore this causes viral translation to be preferred over cellular translation
shuts out host translational and allow viral translation
In what amounts are rotavirus proteins and mRNA made and when during the infection?
mRNAs are made in different amounts early during infection, this indicates each fragment is transcribed independently
late in the infection the level of mRNAs are nearly equivalent, but the protein levels are vastly different
Why do protein levels vary in Rotavirus translation
late in the infection the level of mRNAs are nearly equivalent , but the protein levels are vastly different because,
translation efficiency so the initial production of the proteins
the different proteins could be degraded or not be degraded
How are NSP5 and NSP6 translated on the same mRNA from the 11th segment of the rotavirus genome? Explain the process
NSP5 and NSP6 are translated on the same mRNA by LEAKY SCANNING
NSP5 and NSP6 are in different reading frames and are not the same lengths
the first AUG start codon is not optimal for translation (the majority of the time) therefore the ribosome BYPASSES the first AUG and moves to the second
slipping is DIFFERENT than bypassing
How is human DNA replicated?
semi-conservatively which means that both strand separated and both are replicated
How was Reovirus and Rotavirus genome replication discovered
conservative replication: only one strand is replicated
Michael Schonberg and colleagues tested the genome replication between conservative and semi-conservative in 1971 using radioisotopes that can be measured
+ strand acts as mRNA for protein translation and as a template for genome replication
What type of infection do Reovirues cause
may cause mild infections of the upper respiratory tract and gastrointestinal tract of humans
What are the different types of RNA virus genomes
+ssRNA also called positive sense
-ssRNA also called negative sense or anti or minus strand
dsRNA which has one + sense and one - sense RNA
How does +ssRNA viruses synthesis
can serve as mRNA in protein synthesis
How does -ssRNA viruses synthesis
REQUIRES transcription of + strand RNA for protein synthesis
How does dsRNA viruses synthesis
genome has both + and - sense RNA
Are these segmented or non-segmented?
+ssRNA viruses
-ssRNA viruses
dsRNA virus
+ssRNA predominantly non-segmented
-ssRNA may be segmented or non-segmented
dsRNA ONLY segmented
What is the size range of RNA virus? What are the upper and lower limits correspond to
between 6kb and 41kb
lower limit: minimal set of proteins, RNA polymerase and structural proteins
upper limit: specifics of RNA replication, no proofreading, a higher error rate
What MUST RNA viruses encode and what way MUST replication proceed
RNA viruses MUST encode an RdRP
Replication MUST proceed from 3’ end of the genome
there are not cellular enzymes that can copy RNA from RNA
all know polymerases (RNA/DNA/RT) move 5’ to 3’
How do RNA viruses replicate and how is replication terminated
Must replicate by a dsRNA intermediated
genome termini end must have some sort of signal such as polyA tail sequence or cis-regulatory elements (sometimes the same at the 5’ and 3’ end of the genome called an inverted repeat)
many RNA viruses genomes contain a cis acting packaging signal
Do RNA viruses require a 5’ cap or 3’ polyA tail
RNA viruses do not require a 5’ cap or 3’ polyA tail
some have both
some have one or the other
some have neither
viruses must find unique ways to get around the requirement for these features of mRNAs that are generally required for translation
What type of infection does the Bluetounge virus cause
it is an orbivirus
transmitted by a biting fly
infects sheep, cattle, goats, and wild ruminants
What is the genome of Picornaviridae
+ssRNA
What is the genome of Flaviviridae
+ssRNA
What is the genome of Coronaviridae
+ssRNA
complex
What is the genome of Caliciviridae
+ssRNA
What is the genome of Togaviridae
+ssRNA
What is the genome of Astroviridae
+ssRNA
What is the genome of Orthomyxoviridae
-ssRNA
What is the genome of Paramyxoviridae
-ssRNA
What is the genome of Filoviridae
-ssRNA
What is the genome of Rhabdoviridae
-ssRNA
What is the genome of Bornaviridae
-ssRNA
What is the genome of Reoviridae
dsRNA
What is the genome of rotavirus family
dsRNA
What is the genome of orbivirus
bluetounge virus
dsRNA
Are dsRNA viruses segmented, non segmented or both
ALL are segmented
