Picornaviruses and Their Structure

Picornavirus Structure

• Picornavirus diameter is approximately 25-30 nm.
• A mature picornavirus virion contains 60 copies of VP1, VP2, and VP3.

Picornavirus RNA

• VPg (Viral Protein genome-linked) is covalently bound to the 5’ end of the picornavirus RNA.
• The 5’ NCR (Non-Coding Region) of picornaviruses contains an Internal Ribosome Entry Site (IRES).
• The IRES element contains a pyrimidine-rich track located 20-15 nucleotides from the AUG initiation codon, which likely functions as a landing pad for the 40S ribosomal subunit.

Genome and Translation

• Picornaviruses have a single-stranded, positive-sense RNA genome.
• The genome encodes a polyprotein.
• The IRES element allows for translation at an internal site away from the 5’ end.
• eIF-4G (Eukaryotic Initiation Factor 4G) is involved in the translation process of picornavirus RNA.

Effects of Infection

• During Picornavirus infection, eIF-4G is cleaved, and eIF-4E is phosphorylated.
• eIF-4A, eIF-4E, and eIF-4G are inhibited, leading to the shutdown of host cell cap-dependent translation.
• The consequence of Picornavirus infection is the inhibition of host cell macromolecular functions.

Virion Assembly

• VP0 (Viral Protein 0) is involved in virion assembly.
• The main function of pentamers is to facilitate the assembly of the picornavirus virion.
• The polyprotein P1 is cleaved into VP0, VP1, and VP3 after synthesis.

Replication

• The VPg protein initiates replication of picornavirus RNAs.
• The VPg protein is also involved in picornavirus RNA synthesis.