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Journal of Virology, February 2001, p. 1697-1707, Vol. 75, No. 4
Program in Infectious Diseases and Immunity,
School of Public Health, University of California, Berkeley,
California 94720
Received 11 September 2000/Accepted 22 November 2000
Using a Tn3-based transposon mutagenesis approach, we
have generated a pool of murine cytomegalovirus (MCMV) mutants. In this study, one of the mutants, RvM27, which contained the transposon sequence at open reading frame M27, was characterized both in tissue
culture and in immunocompetent BALB/c mice and immunodeficient SCID
mice. Our results suggest that the M27 carboxyl-terminal sequence is
dispensable for viral replication in vitro. Compared to the wild-type
strain and a rescued virus that restored the M27 region, RvM27 was
attenuated in growth in both BALB/c and SCID mice that were
intraperitoneally infected with the viruses. Specifically, the titers
of RvM27 in the salivary glands, lungs, spleens, livers, and kidneys of
the infected SCID mice at 21 days postinfection were 50- to 500-fold
lower than those of the wild-type virus and the rescued virus.
Moreover, the virulence of the mutant virus appeared to be attenuated,
because no deaths occurred among SCID mice infected with RvM27 for up
to 37 days postinfection, while all the animals infected with the
wild-type and rescued viruses died within 27 days postinfection. Our
observations provide the first direct evidence to suggest that a
disruption of M27 expression results in reduced viral growth and
attenuated viral virulence in vivo in infected animals. Moreover, these
results suggest that M27 is a viral determinant required for optimal
MCMV growth and virulence in vivo and provide insight into the
functions of the M27 homologues found in other animal and human CMVs as well as in other betaherpesviruses.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.4.1697-1707.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Murine Cytomegalovirus Open Reading Frame M27 Plays
an Important Role in Growth and Virulence in Mice
*
Corresponding author. Mailing address: Program in
Infectious Diseases and Immunity, School of Public Health, 140 Warren
Hall, University of California, Berkeley, CA 94720. Phone: (510)
643-2436. Fax: (510) 642-6350. E-mail:
liu_fy{at}uclink4.berkeley.edu.
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