Molecular biology

VIRION

Enveloped. Usually rounded but can be filamentous. The virions are 90-130 nm in diameter.

GENOME

segmented ssRNA(-) linear genome, encapsidated by nucleoprotein (NP) Contains 8 segments coding for at least 8 proteins. Segments size range from 0.8 to 2.2 kb. Genome total size is about 13.5 Kb.

GENE EXPRESSION

Viral RNA polymerase (PB1, PB2? and PA?) transcribes one mRNA from each genome segment. Transcription is primed by cap cleaved from cellular mRNAS by Cap snatching. mRNA are polyadenylated by the viral polymerase stuttering on a poly U track. Splicing of segment 8 produces proteins P6 and P7.

REPLICATION

NUCLEUS

1. Virus attaches to receptor though and is endocytosed in the host cell.
2. endosome acidification induces fusion of virus membrane with the vesicle membrane; encapsidated RNA segments migrate to the nucleus.
3. Transcription of genomic segments by the viral polymerase produces mRNAs.
4. genomic (-)RNA is replicated through antigenomic (+)RNA intermediate.
5. High level of Matrix protein may induce genomes segments export from nucleus.
6. Virus assembly and budding occurs at the plasma membrane.