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
