Biology Reference
In-Depth Information
tubular structures. However, in this case, disintegration continues
beyond this stage, leading to the exposure and release of the compo-
nents within the tubules.
The components initially revealed are filaments of 16 nm in diame-
ter (Fig. 6d). At higher resolution, the surfaces of the 16 nm filaments,
like those of the 30-40 nm tubules, exhibited a helical geometry. In
addition, the filaments were linearly segmented (Fig. 6d).
With high proteinase K concentrations and longer exposure, a
further disintegration of the virus was promoted. What remained
were long strands of double helical DNA, associated with residual
portions of the 16 nm-diameter filaments (Fig. 6e). As seen in Fig. 6f,
the DNA strands were observed emerging from the segments of the
16 nm tubules, indicating that the DNA is packed within the 16 nm
filaments.
AFM observations from chemical and enzymatic dissection lead to
a novel structural model of the vaccinia virion based on a hierarchy of
observed substructures.
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The double-stranded genomic DNA is encap-
sidated within a segmented protein sheath, forming an extended “fila-
ment” of ~16 nm diameter with a helical surface topography (Fig. 6d).
This filament is in turn enclosed within a 30-40 nm diameter “tubule,”
which also shows a helical topography (Fig. 6c). The ellipsoidal virion
core apparently arises from a folded, condensed arrangement of the
30-40 nm tubules (Fig. 6b) surrounded by a shell heavily studded
with proteins. Proteins visualized attached to the tubules may mediate
folding/compacting of the latter and/or represent vestiges of the
core shell. The condensed tubular mass combines with a 50-70 nm-
diameter domain, and this pairing of core and satellite domain is then
enshrouded by membranes heavily studded by proteins and contain-
ing protrusions and spicules on their surface.
AFM Visualization of Virus-infected Cells
AFM provides an important capability to study mechanisms of cell
infection with viruses. These mechanisms include the membrane
fusion processes that lead to entry and exit of viruses into and out
of the cell, as well as morphological changes of the cell surface
