Molecular biology
VIRION
Non-enveloped, spherical, about 30 nm in diameter, composed of a protein shell surrounding the naked RNA genome. The capsid consists of a densely-packed icosahedral arrangement of 60 protomers, each consisting of 4 polypeptides, VP1, VP2, VP3 and VP4. VP4 is located on the internal side of the capsid.
GENOME
Monopartite, linear, ssRNA(+) genome of 7.3 kb, polyadenylated, composed of a single ORF encoding a polyprotein. Viral genomic RNA has a viral protein (VPg) at its 5’ end instead of a methylated nucleotide cap structure. The 5’ end contains an internal ribosome entry site (IRES) probably of type IV. The P1 region encodes the structural polypeptides. The P2 and P3 regions encode the nonstructural proteins associated with replication. Probably encodes a unique protease 3C.
GENE EXPRESSION
The virion RNA is infectious and serves as both the genome and viral messenger RNA. The IRES allows direct translation of the polyprotein that is subsequently processed into the functional products. Protein 2A may cause ribosomes to skip formation of a peptide bond at the junction of the 2A and downstream sequence.
REPLICATION
CYTOPLASMIC
- Virus attaches to host receptors, inducing a capsid conformational change.
- The capsid opens a pore in the host cell membrane, and the viral genomic RNA penetrates into the host cell cytoplasm.
- VPg is removed from the viral RNA, which is then translated into a processed polyprotein.
- Replication of viral RNA takes place on membrane vesicles derived from the ER. A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
- New genomic RNA synthesized using the negative-sense RNA as a template is believed to be packaged into preformed procapsids.
- Cell lysis and virus release.