COMPLEMENTATION OF M-GENE MUTANTS OF VESICULAR STOMATITIS-VIRUS BY PLASMID-DERIVED M-PROTEIN CONVERTS SPHERICAL EXTRACELLULAR PARTICLES INTO NATIVE BULLET SHAPES
Ds. Lyles et al., COMPLEMENTATION OF M-GENE MUTANTS OF VESICULAR STOMATITIS-VIRUS BY PLASMID-DERIVED M-PROTEIN CONVERTS SPHERICAL EXTRACELLULAR PARTICLES INTO NATIVE BULLET SHAPES, Virology, 217(1), 1996, pp. 76-87
The matrix (M) protein of vesicular stomatitis virus (VSV) binds the n
ucleocapsid to the cytoplasmic surface of the host plasma membrane dur
ing virus assembly by budding. It also condenses the nucleocapsid into
a tightly coiled nucleocapsid-M protein complex that appears to give
the virion its bullet-like shape. As described here, temperature-sensi
tive (ts) M mutants produced two classes of membrane-containing extrac
ellular particles al the nonpermissive temperature. These could be dis
tinguished by sedimentation in sucrose gradients and by electron micro
scopy. One class contained nucleocapsids and envelope glycoprotein, bu
t very little M protein. The other class was devoid of nucleocapsids.
Most of these particles were spherical or pleiomorphic in shape as det
ermined by electron microscopy. Expression of wild-type (wt) M protein
from plasmid DNA using the vaccinia/T7 virus system did not enhance t
he incorporation of nucleocapsids into extracellular particles from ce
lls coinfected with the ts M mutants but did enhance the incorporation
of M protein into these particles. Electron microscopy showed that wt
M protein served to impart the bullet-like shape typical of VSV virio
ns to what would otherwise be spherical or pleiomorphic virus-like par
ticles. These data suggest that there are two distinct processes in VS
V envelope biogenesis. One process involves envelopment of the nucleoc
apsid and can be accomplished by the ts M mutants at the nonpermissive
temperature, albeit at a low level compared to wt VSV. The other proc
ess involves conversion of virion components into the bullet-like shap
e and requires a function provided by wt M protein. (C) 1996 Academic
Press, Inc.