Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 135

Viruses with (–) strand RNA genomes are found in 19 families. These genomes are linear and may be single molecules (nonsegmented; some viruses with this configuration have been classified in the order Mononegavirales) or segmented. Viruses of this type that can infect vertebrates include members of the Arenaviridae, Bornaviridae, Filoviridae, Hantaviridae, Orthomyxoviridae, Paramyxoviridae, Pneumoviridae, and Rhabdoviridae families. Unlike (+) strand RNA, (–) strand RNA genomes cannot be translated directly into protein but must be first copied to make (+) strand mRNA. There are no enzymes in the cell that can make mRNAs from the RNA genomes of (–) strand RNA viruses. These virus particles therefore contain virus-encoded RNA-dependent RNA polymerases. The genome is also the template for the synthesis of full-length (+) strands, which, in turn, are copied to produce (–) strand genomes.

Figure 3.7 Structure and expression of viral single-stranded (+) RNA genomes with a DNA intermediate. (A) Synthesis of genomes, mRNA, and protein. (B) Genome configuration.

Figure 3.8 Structure and expression of viral single-stranded (–) RNA genomes. (A) Synthesis of genomes, mRNA, and protein. The icon represents an orthomyxovirus particle. (B and C) Genome configurations.

The genomes of certain (–) strand RNA viruses (e.g., members of the Arenaviridae and Bunyaviridae) are ambisense: they contain both (+) and (–) strand information on a single strand of RNA (Fig. 3.8C). The (+) sense information in the genome is translated upon entry of the viral RNA into cells. Replication of the RNA genome yields additional (+) sense sequences, which are then translated.