Picornaviridae Flashcards
Which order does the family picornaviridae belong to?
Order Picornavirales
What features do all viruses in the order share?
Conserved RNA-dependent RNA polymerase, protein VpG attached to the 5’ end, absence of overlapping ORFs within the genome, viral RNA translated into a polyprotein before processing.
Which genus does FMD belong to?
Aphthovirus
What are the virion properties of picornaviruses?
Non-enveloped, 30nm in diameter, icosahedral symmetry. Smooth and round in electron microscopy. Genome is a single molecule of linear, positive sense, ss RNA, 7-8.8kb in size.
Where is the VPg protein?
VPg is linked covalently to the 5’ end, making the RNA infectious.
What proteins make the capsid of picornaviruses, and where are the host-cell receptors?
60 copies of 4 capsid proteins (VP1, VP2, VP3, and VP4) and one copy of VPg. Host-cell receptors are located in VP1.
Explain replication of picornaviruses, using FMD as model and explaining differences with polio.
Cell receptor of FMD are integrins or heparan sulfate (cell culture), Once it binds, enters through clathrin dependent endosomal pathway. This differs from polio which goes through conformational changes of its VP4 and VP1 prot, producing pores in cell mb that perits entrance of RNA. Viral gene products are preferentially translated while cell products are stopped. Initiation of translation occurs in the internal ribosome entry segment (IRES), a section of viral genomic RNA. The RNA has only 1 ORF, tranlated to 1 protein which is later cleaved to 11 or 12 prot. RNA synthesis is done in a replication complex using VPg as primer. The complex contains replication intermediates, with full length negative RNA, which is transcribed to positive sense by RNA polymerase. L prot makes viral mRNA to be translated preferentially, making viral replication very effective. Large paracrystalline arrays of virus can be seen accumulating in cells.
