negative strand rna synthesis

Negative strand RNA synthesis

- 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

Vesicular Stomatitis Virus (VSV)

The VSV Genome

Uses of – sense template

• Capping and polyadenylation mechanism of viral RNA different to host mRNA and is carried out by host encoded enzymes.

Switch from translation to replication

Influenza Virus Segmented – sense RNA

The genome

Marking strands for packaging

N Protein

• 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.

Capping from host mRNA (cap snatching)

RNA synthesis from dsRNAgenomes

dsRNA viruses• Contain dsRNA segmented genomes• Viral polymerase

Adapted from D. R. Harper. Molecular Virology, Second Edition. BIOS Scientific Publishers, 1999.

Figure 3.10: List of dsRNA viruses and their replication strategy.

The genome

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