Studies on the Structure of Vaccinia Virus

Abstract

SUMMARYVaccinia virus has been examined with the electron microscope by several techniques in conjunction with experimental modifications of structure. Negative staining revealed that over 80 yo of the virus in highly purified preparations were particles which appeared to have a beaded surface like a mulberry and were termed M forms. The beading was formed by loops of thread-like structures 9 0 6 wide which were themselves double helices formed from two 8oA strands coiled to a 1206 pitch.Twenty per cent or less of the particles appeared as larger more electrondense bodies with a capsule of complex structure; these have been termed C forms. Experimental interconversion of the two forms showed that both were structurally mature virus. The relationship of structures seen in C forms to those revealed by thin sectioning is considered. Experimental findings and the results of shadowing and replica examinations indicate the presence of a superficial protein layer of antigenic material not revealed by negative staining. The relationship of this layer to the structure of the virus and the nature of the ribbon structure of the M form are discussed.

Structure of Intracellular Mature Vaccinia Virus Visualized by In Situ Atomic Force Microscopy

“…4c and 5a and b). This is consistent with EM data (9) showing that viral cores possess a ϳ9-nm-thick electron-translucent outer shell (also described as a wall) decorated on the outside with what have been variously described as spicules, pegs (9), or a palisade layer (6) protruding from the core wall by ϳ10 to 20 nm (9,26,41). The core wall is probably composed, in large part, of vaccinia virus proteins p4a and p4b (32), and the pegs may contain vaccinia virus protein p39/A4L (3, 33) as indicated by EM immunolocalization studies.…”

“…Virion features prominent in conventional EM images, such as membranous surface tubules (30,31), ridges (4), threads (29), helices (41), as well as lateral bodies and a dumbbell shape for the core, were not visible in cryo-EM images of the intact virion (6), indicating that they may have been artifacts resulting from virion dehydration and nonisotropic collapse during sample preparation. Nonetheless, structures reminiscent of the lateral bodies have been observed in some recent cryo-EM studies (12,13), and the dumbbell shape has been argued to be bona fide, with its visualization dependent upon virion orientation during sectioning or vitrification.…”

“…The structure of the vaccinia virus virion has been the subject of electron microscopy (EM) studies (comprehensively reviewed in reference 10) extending over half a century, encompassing shadowing, thin sectioning, freeze-etching, and negative staining techniques (9,15,26,(29)(30)(31)(32)(40)(41)(42). The virion was initially described (10) as brick shaped with dimensions of approximately 300 by 230 nm, with inner and outer membranes sandwiching a pair of lateral bodies and enclosing a central core containing the genomic DNA.…”

The Envelope of Vaccinia and Orf Viruses: an Electron-cytochemical Investigation

“…The ridged form was also significantly smaller than the 'C' form (2P o-oo5; Table 3)- Table 4 and text. Grids were viewed within 4 hr of preparation (see Harris & Westwood, 1964). …”

Atomic Force Microscopy Investigation of Vaccinia Virus Structure

“…Nonetheless, despite ϳ60 years of study by conventional electron microscopy (EM) (11,14,15,45,48,54,58), cryoelectron microscopy (1, 9, 54), and more recently cryoelectron tomography (4) freeze etch (31), deep etch (11), and atomic force (22) microscopies, specific controversies remain in issues such as the intrinsic rigidity of the core, the degree of order in genome packaging, the degree and affinity of the association of the genome with protein in the packaged state, the presence/absence of an "inner membrane" or "palisade" enwrapping the core, and the number of lipid bilayers that enwrap the intact virion. Structural details of the virion are relevant to several stages of the vaccinia life cycle, including mechanisms of fusion and entry, extrusion of early mRNA from the infecting virion, disassembly of the infecting virion, genome packaging into nascent virions during assembly, and virion maturation/membrane enwrapment.…”