Journal of Virology, October 1998, p. 7885-7894, Vol. 72, No. 10
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


Departments of Biomedical
Sciences1 and
Biological
Sciences,
Received 20 April 1998/Accepted 8 July 1998
Expression studies have shown that the coronavirus small envelope
protein E and the much more abundant membrane glycoprotein M are both
necessary and sufficient for the assembly of virus-like particles in
cells. As a step toward understanding the function of the mouse
hepatitis virus (MHV) E protein, we carried out clustered charged-to-alanine mutagenesis on the E gene and incorporated the
resulting mutations into the MHV genome by targeted recombination. Of
the four possible clustered charged-to-alanine E gene mutants, one was
apparently lethal and one had a wild-type phenotype. The two other
mutants were partially temperature sensitive, forming small
plaques at the nonpermissive temperature. Revertant analyses of these
two mutants demonstrated that the created mutations were responsible for the temperature-sensitive phenotype of each and provided support for possible interactions among E protein monomers. Both temperature-sensitive mutants were also found to be markedly thermolabile when grown at the permissive temperature, suggesting that
there was a flaw in their assembly. Most significantly, when virions of
one of the mutants were examined by electron microscopy, they were
found to have strikingly aberrant morphology in comparison to the wild
type: most mutant virions had pinched and elongated shapes that
were rarely seen among wild-type virions. These results demonstrate an
important, probably essential, role for the E protein in coronavirus
morphogenesis.
*
Corresponding author. Mailing address: David Axelrod
Institute, Wadsworth Center, NYSDOH, New Scotland Ave., P.O. Box 22002, Albany, NY 12201-2002. Phone: (518) 474-1283. Fax: (518) 473-1326. E-mail: masters{at}wadsworth.org.
Present address: LaboRétro, INSERM U412, ENS, 46 allee
d'Italie, 69364 LYON cedex 07, France.
Present address: Physiologisch-chemisches Institut, Universitaet
Tuebingen, Germany.
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