- Sense RNA genomes • Unimolar • Segmented
What does segmented mean? • Genome in segments often representing different genes. • Segmented genomes confer evolutionary advantages. • Different strains of a virus with a segmented genome can shuffle and combine genes and produce progeny viruses or (offspring) that have unique characteristics. • This is called reassortment
Capping and polyadenylation mechanism of viral RNA different to host mRNA and is carried out by host encoded enzymes.
Nucleocapsids are transported into the nucleus. • mRNA synthesis and replication of viral RNA occurs in the nucleus. • This is very unusual for an RNA virus. Influenza virus has an unusual mechanism for acquiring a methylated, capped 5'end to its mRNAs. • A viral endonuclease (which is packaged in the influenza virus) snips off the 5'end of a host capped, methylated mRNA about 13-15 bases from the 5' end and uses this as a primer for viral mRNA synthesis. • Hence all flu mRNAs have a short stretch at the 5' end which is derived from host mRNA.
dsRNA viruses • Contain dsRNA segmented genomes • Viral polymerase Figure 3.10: List of dsRNA viruses and their replication strategy. Adapted from D. R. Harper. Molecular Virology, Second Edition. BIOS Scientific Publishers, 1999.
Negative Strand Viruses • Contain enzymes for transcription in virion • Make mRNA prior to antigenome • Message gets capped; genome does not • Plus strand is template for minus strand genome • Makes more minus than plus strand