Zika virus (taxid:64320)

VIRION

Enveloped, spherical, about 50 nm in diameter. The surface proteins are arranged in an icosahedral-like symmetry.

GENOME

Monopartite, linear, ssRNA(+) genome of of 10,794 bp. The genome 5' end has a methylated nucleotide cap for canonical cellular translation. The 3' terminus is not polyadenylated but forms a loop structure. This secondary structure leads to the formation of a subgenomic flavivirus RNA (sfRNA) through genomic RNA degradation by host XRN1. sfRNA is essential for pathogenicity, and may play a role in inhibiting host RIG-I antiviral activity as shown for Dengue virus

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and the viral messenger RNA. The whole genome is translated in a polyprotein 3,419 aa long, which is processed co- and post-translationally by host and viral proteases. An upstream ORF (uORF) mediates polyprotein translation and would play a role in virus neurotropism .

ENZYMES

• RNA-directed RNA polymerase [NS5]
• Cell-type capping
  • RNA TPAse [NS3]
  • GTase, N7Mtase, 2'O methylase [NS5]
• Polyprotein major protease (Peptidase S7) [NS3]

REPLICATION

CYTOPLASMIC in mammals, NUCLEAR in insects?

1. Attachement of the viral envelope protein E to host receptors mediates internalization into the host cell by apoptotic mimicry
2. Fusion of virus membrane with host endosomal membrane. RNA genome is released into the cytoplasm.
3. The positive-sense genomic ssRNA is translated into a polyprotein, which is cleaved into all structural and non structural proteins (to yield the replication proteins).
4. Replication takes place at the surface of endoplasmic reticulum in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Virus assembly occurs at the endoplasmic reticulum. The virion buds at the endoplasmic reticulum and is transported to the Golgi apparatus.
7. The prM protein is cleaved in the Golgi, thereby maturing the virion which is fusion competent.
8. Release of new virions by exocytosis.