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J. Virol., 08 1995, 4640-4648, Vol 69, No. 8
D Rodriguez, M Esteban and JR Rodriguez
Vaccinia virus (VV) A17L gene encodes a 23-kDa protein that is
proteolytically cleaved to generate a 21-kDa product that is incorporated
into the viral particles. We have previously shown that the 21-kDa protein
forms a stable complex with the VV 14-kDa envelope protein and suggested
that the 21-kDa protein may serve to anchor the 14-kDa protein to the
envelope of the virion (D. Rodriguez, J. R. Rodriguez, and M. Esteban, J.
Virol. 67:3435-3440, 1993). To study the role of the 21-kDa protein in
virion assembly, in this investigation we generated a VV recombinant,
VVindA17L, that contains an inducible A17L gene regulated by the E. coli
repressor/operator system. In the absence of the inducer, shutoff of the
A17L gene was complete, and this shutoff correlated with a reduction in
virus yields of about 3 log units. Although early and late viral
polypeptides are normally synthesized in the absence of the A17L gene
product, proteolytic processing of the major p4a and p4b core proteins was
clearly impaired under these conditions. Electron microscopy examination of
cells infected in the absence of isopropylthiogalactopyranoside (IPTG)
revealed that virion morphogenesis was completely arrested at a very early
stage, even prior to the formation of crescent-shaped membranes, which are
the first distinguishable viral structures. Only electron-dense structures
similar to rifampin bodies, but devoid of membranes, could be observed in
the cytoplasm of cells infected with VVindA17L under nonpermissive
conditions. Considering the most recent assembly model presented by Sodeik
et al. (B. Sodeik, R. W. Doms, M. Ericsson, G. Hiller, C. E. Machamer, W.
van't Hof, G. van Meer, B. Moss, and G. Griffiths, J. Cell Biol.
121:521-541, 1993), we propose that this protein is targeted to the
intermediate compartment and is involved in the recruitment of these
membranes to the viral factories, where it forms the characteristic
crescent structures that subsequently result in the formation of virions.
Copyright © 1995, American Society for Microbiology
Vaccinia virus A17L gene product is essential for an early step in virion morphogenesis
Department of Molecular and Cellular Biology, Universidad Autonoma, Madrid, Spain.
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