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have a non-enveloped, icosahedral capsid that encloses a ssRNA that is positive sense
60 copies of four proteins: VP1-4
How do VP1-3 arrange themselves?
they arrange themselves in a wedge-shaped jelly-roll, composed of an eight-stranded Beta-barrel structure
they form the capsid shell
What are some ways of entry for picornaviruses?
rhinoviruses: receptor-mediated endocytosis
others bind to a receptor. They lose VP4 and VP1 is extruded to the cell surface
virus-encoded protein that is covalently attached to the 5' end of genome RNA and a poly(A) tract of 30-100 nucleotides
poly(A) is already part of the genome
Most cellular mRNAs employ what to initiate translation near the 5' end?
employ cap-dependent mechanisms
the eIF-4F complex, with eIF-4A,E, and G recruits a 40S ribosomal subunit to the capped 5' end of an mRNA
the 40S subunit scans the mRNA, searching for AUG. THen, the 60S joins to form the 80S. Protein synthesis begins
How is cap-dependent translation abolished?
proteolytic cleavage of eIF-4G or by sequestration of the cap-binding protein eIF-4E.
Because picornavirus RNA isn't capped, wat is the mechanism used to direct ribosomes to the initiator AUG codon?
they initiate protein synthesis via an IRES that lies within the 5' noncoding region
What is a problem with + RNA viruses?
Their mRNA codes for a single protein. It is a polyprptein that gets cleaved into different fx. polyproteins by proteinases. It is cleaved into P1-3
subsequently cleaved into capsid proteins VP0, 1, and 3
VP0--> VP2 and VP4
What are the three proteinases?
- L: cleaves itself from the VP4 an cleaves eIF-4G
- 2A: cleaves at the P1/P2 junction; cleaves eIF-4G