Fig 1.
Chlorella cells and chlorovirus Paramecium bursaria chlorella virus (PBCV-1).
(A) Paramecium bursaria and its symbiotic chlorella cells. (B) Plaques formed by PBCV-1 on a lawn of Chlorella variabilis. (C) Five-fold averaged cryo-electron micrograph of PBCV-1 reveals a long narrow cylindrical spike structure at one vertex and fibers extending from one unique capsomer per trisymmetron. (D) PBCV-1 attached to the cell wall as viewed by the quick-freeze, deep etch procedure. Note the virions attached to the wall by fibers. (E) Surface view of the PBCV-1 spike structure and fibers. (F) Initial attachment of PBCV-1 to a C. variabilis cell wall. (G) Attachment of PBCV-1 to the algal wall and digestion of the wall at the point of attachment. This occurs within 1–3 minutes postinfection (PI) (H) Virion particles assemble in defined areas in the cytoplasm named virus assembly centers at ~4 hour PI. Note that both DNA containing (dark centers) and empty capsids. (I) A model depicting PBCV-1 assembly into infectious particles including generation of nuclei-derived cisternae decorated with ribosomes (red spheres), which serve as precursors (dark blue) for single bilayer viral membranes (light blue) in the viral assembly centers. (J) Localized lysis of cell plasma membrane and cell wall and release of progeny viruses at ~8 hours PI. This figure is modified with permission: Fig 1A–H and J is modified from reference 2 with permission and Fig I is modified from reference 18 with permission.