Herbevirus

VIRION

Enveloped, spherical. Diameter from 80 to 120nm.

GENOME

Segmented Negative-stranded RNA linear genome, L segment is about 6.9kb, M segment about 4.5kb and S segment about 1kb.
Encodes for six proteins.

GENE EXPRESSION

Transcription starts by viral RNA dependent RNA polymerase (L) binding to a promoter on each encapsidated segment, and is terminated by a strong hairpin sequence at the end of each gene. mRNAs are capped by L protein during synthesis using cap snatching ., but are not polyadenylated.

S segment encodes for NSs protein by leaky scanning. M segment encodes for a polyprotein which is cleaved by host protease into Gn, NSm and Gc proteins.

REPLICATION

CYTOPLASMIC

  1. Virus attaches to host receptors though Gn-Gc glycoprotein dimer, and is endocytosed into vesicles in the host cell.
  2. Fusion of virus membrane with the vesicle membrane; ribonucleocapsid segments are released in the cytoplasm.
  3. Transcription, viral mRNAs are capped in the cytoplasm.
  4. Replication presumably starts when enough nucleoprotein is present to encapsidate neo-synthetized antigenomes and genomes.
  5. The ribonucleocapsids buds at Golgi apparatus, releasing the virion by exocytosis.

Host-virus interaction

Inhibition of host transcription initiation

The Bunyamwera virus (BUNV) NSs protein plays a role in the inhibition of host RNA polymerase II