FIG. 5.

The core shell and the aberrant zipper-like structures are structurally and biochemically related. Cells infected with parental BA71V (A, B, C, D, and E) and recombinant vA72 (F, G, H, and I) were processed by conventional Epon embedding at 16 to 24 hpi. (A to E) Different stages of the assembly of an intracellular mature particle. Note that the assembly of the core shell (indicated by three parallel lines) beneath the inner envelope is concomitant with the formation of the outer capsid (A) and precedes the maturation of the DNA-containing nucleoid (B to D). Note also that the fine electron-dense layer that subdivides the core shell is less evident in intracellular mature virions (E). (F and G) Aberrant zipper-like structures assembled at vA72 virus factories at 16 hpi under restrictive conditions. Zipper-like elements consist of a core shell-like structure limited by two inner envelopes (G). (H and I) Icosahedral aberrant viruses formed in vA72-infected cells maintained for 16 h under restrictive conditions and then treated with inducer for an additional 8-h period. Note that the zipper elements become icosahedral, double-enveloped particles after capsid assembly (arrowhead in panel H) on one of the two flanking envelopes. Note also that the core shell of these particles (I) is nearly identical to that of normal assembling virions (B to D). (J) A diagram illustrates the similarities and differences between a normal (right half) and an aberrant (left half) particle. Note that the aberrant particle contains an additional innermost lipid envelope but lacks the nucleoid. (K and L) Immunogold labeling of vA72-infected cells maintained under restrictive conditions for 24 h. Lowicryl sections were labeled with anti-pp62 (K) or anti-pp220 (L) antibodies followed by protein A-gold (10-nm diameter). c, capsid; ie, inner envelope; cs, core shell; n, nucleoid. Bars, 100 nm.