Negative strand RNA synthesis
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Transcript of Negative strand RNA synthesis
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Negative strand RNA synthesis
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- Sense RNA genomes
• Unimolar• Segmented
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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
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Vesicular Stomatitis Virus (VSV)
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The VSV Genome
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Uses of – sense template
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• Capping and polyadenylation mechanism of viral RNA different to host mRNA and is carried out by host encoded enzymes.
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Switch from translation to replication
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Influenza Virus Segmented – sense RNA
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The genome
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Marking strands for packaging
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N Protein
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• 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.
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Capping from host mRNA (cap snatching)
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RNA synthesis from dsRNAgenomes
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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.
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The genome
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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