general considerations of RNA viruses
a group of viruses with genomes that can serve as mRNA and use DNA as the intermediate in their replication
what does the replication of poliovirus provide?
a basic model for RNA virus replication
how is zika virus transmitted?
Aedes aegypti mosquitoes
what is the virus entry for coronaviruses?
virus entry is by receptor- mediated fusion of the vision with the plasma membrane, followed by the release of genomic RNA.
what is the structure of the tobacco mosaic virus?
what do positive sense RNA viruses NOT require prior to viral protein expression?
a transcription step
for poliovirus, what did full characterization and sequence analysis establish?
the genome is 7741 bases long with a very long (743 base) leader sequence between the 5' end of the mRNA and the AUG, which initiates the beginning of an ORF extending to a translation termination signal near the 3' end.
what does the structural protein precursor for flavivirus include?
an integral membrane protein and an envelope glycoprotein
what makes the structure of a coronavirus unusual for a positive- sense RNA virus?
the helical nucleocapsid is unusual for a positive- sense RNA virus
what do all of the positive-sense plant RNA viruses have?
all of the positive-sense plant RNA viruses have genomes that can be translated entirely or in part immediately after infection.
what it error frequency and what are some reasons for it to be as high as 10^4 for some RNA genomes?
Error frequency is the frequency of incorporating an incorrect base. Part of the reason for this error rate for RNA is because there is truly double- stranded intermediate. A second reason is that RNA polymerases using RNA using RNA templates seem to have an inherently higher error frequency than those using DNA.
what two properties does polio RNA have that make it different from cellular mRNA?
Poliovirus vision RNA has a protein VPg and its 5' end instead of the methylated cap structure found in cellular mRNA. The viral mRNA also has a very long leader that can assume a complex structure by virtue of intramolecular base paring in a solution.
what is the structure of the flavivirus genome?
the flavivirus genome is over 10,000 bases long, and unlike poliovirus, it is capped at the 5' end and not polyadenylated at the the 3' end.
where does the 30- kb coronavirus genome encode and what is it the template for?
at eight separate translational reading frames, and is the template for the synthesis of at least seven subgeneric mRNA's.
what is the added complication that comes with positive- sense RNA plant genomes?
what is the term "quasi- species swarm" applied to?
virus stocks generated from a single infectious event
it is stated that poliovirus only has one "gene" because the poliovirus ORF is translated as a single large protein. Why is this not strictly true?
since different portions of the ORF contain information for different types of protein or enzyme activities.
why is sinus virus a well studied example when studying virus replication?
it has a similar structure to flaviviruses and picornaviruses. The capsid is enveloped, and its viral genome contains two translational ORF's.
what are the two competing models that have been presented for coronavirus transcription?
Leader-primed transcription: the replication proteins first produce a full- length negative-strand copy of the genome using a standard RI-1 structure
Discontinuous transcription: the replication proteins transcribe negative- strand copies of the genome using a standard RI-1 structure
How is the structure of RNA bacteriophages described?
linear, single stranded, positive- sense genomes enclosed within small isohedreal capsids
what stages do single stranded RNA virus genomes require for replication?
First, the input strand must be transcribed (using Watson- Crick base paring rules), into a strand of complementary sequence and opposite polarity. Replication occurs as a "fuzzy", multi branched structure. The whole RNP is termed the type 1 replicative intermediate (RI-1). The complementary strand RNA serves as a template for the formation of more genomic- sense RNA strands. The second replicative intermediate (RI-2) is essentially the same, except it is of opposite sense to genomic RNA and nascent product RNA molecules are of genome sense.
the final steps of maturation of the capsid.
What does the M protein contain?
The M protein contains a "signal" sequence at it's N- terminal that facilitates the insertion of the nascent peptide chain into the endoplasmic reticulum.
what is the importance regarding angiotensin- converting enzyme 2 (ACE2)?
SARS- CoV utilizes ACE2 as a receptor to initiate viral entry into the cytoplasm of the infected cell. ACE 2 converts angiotensin from a form that induces tissue damage and lung edema into a form of the protein that is more benign.
Bacterial ribosomes can initiate translation at start sites in the interior of bacterial mRNA. what does this mean?
this means that a bacterial mRNA molecule with several ORF's can be translated independently into one or all of the proteins.