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J. Virol., Jan 1998, 294-302, Vol 72, No. 1
E Herrera, M del Mar Lorenzo, R Blasco and SN Isaacs
Vaccinia virus has two forms of infectious virions: the intracellular
mature virus and the extracellular enveloped virus (EEV). EEV is critical
for cell-to-cell and long-range spread of the virus. The B5R open reading
frame (ORF) encodes a membrane protein that is essential for EEV formation.
Deletion of the B5R ORF results in a dramatic reduction of EEV, and as a
consequence, the virus produces small plaques in vitro and is highly
attenuated in vivo. The extracellular portion of B5R is composed mainly of
four domains that are similar to the short consensus repeats (SCRs) present
in complement regulatory proteins. To determine the contribution of these
putative SCR domains to EEV formation, we constructed recombinant vaccinia
viruses that replaced the wild-type B5R gene with a mutated gene encoding a
B5R protein lacking the SCRs. The resulting recombinant viruses produced
large plaques, indicating efficient cell-to-cell spread in vitro, and
gradient centrifugation of supernatants from infected cells confirmed that
EEV was formed. In contrast, phalloidin staining of infected cells showed
that the virus lacking the SCR domains was deficient in the induction of
thick actin bundles. Thus, the highly conserved SCR domains present in the
extracellular portion of the B5R protein are dispensable for EEV formation.
This indicates that the B5R protein is a key viral protein with multiple
functions in the process of virus envelopment and release. In addition,
given the similarity of the extracellular domain to complement control
proteins, the B5R protein may be involved in viral evasion from host immune
responses.
Copyright © 1998, American Society for Microbiology
Functional analysis of vaccinia virus B5R protein: essential role in virus envelopment is independent of a large portion of the extracellular domain
Department of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
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