Figure 1 (Left) Cryo-electron microscopic reconstruction of Saccharomyces cerevisiae virus L-A (ScV-L-A) at 16 Å resolution (Caston et al.). The view shown is along a 5-fold axis of the icosahedral particles. (Right) Negative contrast electron micrograph of Helminthosporium victoriae virus 190S (HvV-190S) virions, a representative species in the genus Totivirus. The bar represents 50 nm.
Figure 2 Genome organization of Saccharomyces cerevisiae virus L-A (ScV-L-A). The virion-associated RNA polymerase catalyzes in vitro end-to-end transcription of dsRNA by a conservative mechanism to produce mRNA for capsid proteins. In the case of ScV-L-A, all of the positive strand transcripts are extruded from the particles. The positive strand of satellite RNA M1, or deletion mutants of L-A or M1, on the other hand, often remain within the particle where they are replicated to give two or more dsRNA molecules per particle (headful replication). The positive ssRNA of ScV-L-A is the species encapsidated to form progeny virus particles. The encapsidation signal on ScV-L-A or M1 positive sense ssRNA is a 24 b stem-loop sequence located 400 nts from the 3-end in each case. The Gag protein must be acetylated (by the cellular Mak3p) for assembly and packaging to proceed. These particles have a replicase activity that synthesizes the negative strand on the positive strand template to produce dsRNA, thus completing the replication cycle. Replication requires an internal site overlapping with the packaging signal, and a specific 3-end sequence and secondary/tertiary structure. Virions accumulate in the cytoplasm.
Figure 3 Negative contrast electron micrograph of Giardia lamblia virus (GLV) virions. TMV is included as an internal size marker. The bar represents 100 nm.
Figure 4 Negative contrast electron micrograph of Leishmania RNA virus 1 - 1 (LRV1-1) virions. The bar represents 100 nm.
Figure 5 Genome organization of Leishmania RNA virus 1 - 1 (LRV1-1).
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