Molecular biology

VIRION

Non-enveloped, flexuous and exceptionally long, filamentous particles about 950-2200 nm in length and 10-13 nm in diameter. The virion body is assembled by the major capsid protein (CP) and the tail by the minor capsid protein (CPm).

GENOME

Mono-(Ampelovirus, Closterovirus) or bi-partite (Crinivirus), linear, ssRNA(+) genome of 15 to 20 kb. 3’ terminus has no poly(A) tract and the 5’ terminus probably has a methylated nucleotide cap.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. An alternative ribosomal frameshift at the end of ORF1a produces the RdRp ORF1ab protein. Other ORFs are translated from a set of nested 3’ co-terminal subgenomic RNAs.

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the host cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. The viral RNA is translated.
4. Negative-sense complementary ssRNAs are synthesized using the genomic RNAs as a templates.
5. New genomic RNAs are synthesized using the negative-sense RNAs as templates.
6. Formation of new virus particles.