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Journal of Virology, October 2001, p. 9762-9770, Vol. 75, No. 20
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.20.9762-9770.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Functional Roles of Equine Infectious Anemia Virus
Gag p9 in Viral Budding and Infection
Chaoping
Chen,
Feng
Li, and
Ronald C.
Montelaro*
Department of Molecular Genetics and
Biochemistry, University of Pittsburgh School of Medicine,
Pittsburgh, Pennsylvania 15261
Received 16 May 2001/Accepted 16 July 2001
Previous studies utilizing Gag polyprotein budding assays with
transfected cells reveal that the equine infectious anemia virus (EIAV)
Gag p9 protein provides a late assembly function mediated by a critical
Y23P24D25L26 motif
(L-domain) to release viral particles from the plasma membrane. To
elucidate further the role of EIAV p9 in virus assembly and
replication, we have examined the replication properties of a defined
series of p9 truncation and site-directed mutations in the context of a
reference infectious molecular proviral clone, EIAVuk.
Characterization of these p9 proviral mutants revealed new functional
properties of p9 in EIAV replication, not previously elucidated by Gag
polyprotein budding assays. The results of these studies
demonstrated that only the N-terminal 31 amino acids of a total of 51 residues in the complete p9 protein were required to maintain
replication competence in transfected equine cells; proviral mutants
with p9 C-terminal truncations of 20 or fewer amino acids remained replication competent, while mutants with truncations of 21 or more
residues were completely replication defective. The inability of the
defective p9 proviral mutations to produce infectious virus could not
be attributed to defects in Gag polyprotein expression or
processing, in virion RT activity, or in virus budding. While proviral
replication competence appeared to be associated with the presence of a
K30K31 motif and potential ubiquitination of the EIAV p9 protein, mutations of these lysine residues to methionines produced variant proviruses that replicated as well as the parental EIAVuk in transfected ED cells. Thus, these observations
reveal for the first time that EIAV p9 is not absolutely required for virus budding in the context of proviral gene expression, suggesting that other EIAV proteins can at least in part mediate late budding functions previously associated with the p9 protein. In addition, the
data define a function for EIAV p9 in the infectivity of virus particles, indicating a previously unrecognized role for this Gag
protein in EIAV replication.
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Biochemistry, University of Pittsburgh School of
Medicine, W1144 Biomedical Science Tower, Pittsburgh, PA 15261. Phone:
(412) 648-8869. Fax: (412) 383-8859. E-mail: rmont{at}pitt.edu.
Journal of Virology, October 2001, p. 9762-9770, Vol. 75, No. 20
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.20.9762-9770.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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