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naked icosahedral capsids and twelve spikes (T=1 symmetry)
overlapping genes that allows more genes to be synthesized
Explain the genome of microviruses.
1) a circle of ssDNA that is really small only the size of a plasmid
2) unlike other viruses, it has three different promoters due to the overlap of open reading frames
What is interesting about the discovery of microviruses?
it was the first time they found ssDNA; it was like a black swan
Microviruses depend on __ to synthesize their mRNAs. BEcuase cellular RNA polymerases require double stranded DNA template, the microviruses must do what and how?
transform their ssDNA genome into double stranded DNA before viral genes can be transcribed
intracellular page DNA is coated everywhere by single stranded DNA binding proteins in all plces but a "hairpin" region. This region serves as a signal for the assembly of a primosome
What does the primosome do?
enables primase to gnerate short comp. RNA primers at different locations around the single-stranded phage DNA. DNA polymerase then makes a complementary copy of DNA. A ligase then joins the DNA chains after removal of the primers
After a replicative form of DNA is synthesized, what happens next?
it is amplified by the rolling circle mechanism
Explain the rolling circle mechanism.
1) The viral A protein binds and clieves the plus-strand on replicative form DNA at a specific site and is covalently linked to the resulting 5' end of the DNA via a tyrosine residue in the protein
2) host cell rep protein acts together with the viral A protein as a helicase to unwind the plus-strand from its association with its complementary minus-strand
3) DNA polymerase extends the strand created by cleavage of the plus strand, thereby synthesizing more plus-strand DNA
4) cleavage occurs as the plus strand is cut and ligated to form a single-strand circle
5) the second phase is formation of a more replicative form DNA from teh progeny viral DNA
what is the burst size?
it is the number of viruses produced by that cell and is characteristic of the virus
how many can be made before release
Microvirus has what in addition to its very small genome?
it has extras, encoding different scaffolding proteins--proteins that help the actual structure of the virus come together to form the viral particle; allows the actual capsid and spike proteins to come together more quickly
What is the microvirus's strategy?
speed. It does what it has to before the cell has the power to fight back
Explain the overlapping genes.
the genes that are tucked into other genes tend to be the ones that are not super required to complete a replication cycle of the virus
overlapping decreases the size of the genome as well as increases its fitness
Explain the microvirus evolution
unlike other viruses, they appear to be related to human and plant viruses
How are procapsids assembled?
by the use of scaffolding proteins, which greatly increases speed of virus assembly
the genome DNA is then inserted into procapsids
Explain scaffolding proteins.
they allow a high degree of flexibility