Affiliation:
1. Department of Medicine and Epidemiology, School of Veterinary Medicine
2. Department of Medical Pathology, School of Medicine, University of California, Davis, California 95616
Abstract
ABSTRACT
The
orf-A
(
orf-2
) gene of feline immunodeficiency virus (FIV) is a small open reading frame predicted to encode a 77-amino-acid protein that contains putative domains similar to those of the ungulate lentiviral Tat protein. Orf-A is reported to be critical for efficient viral replication in vitro and in vivo. A series of FIV-pPPR-derived proviruses with in-frame deletions and point mutations within
orf-A
were constructed and tested for replication in feline lymphoid cells. Orf-A mutant proviruses were also tested for viral gene and protein expression, viral particle formation, and virion infectivity. Deletions within
orf-A
severely restricted FIV replication in feline peripheral blood mononuclear cells (PBMC) and interleukin-2-dependent T-cell lines. In addition, substitutions of alanines for leucines in the putative leucine-rich domain, for cysteines in the putative cysteine-rich domain, and for a tryptophan at position 43 in Orf-A restricted the replication of FIV mutants. Deletions and point mutations in
orf-A
imposed a small effect or no effect on FIV long-terminal-repeat-driven viral gene expression and had no effect on viral protein expression. However, release of cell-free, virion-associated viral RNA in supernatants from cells transfected with
orf-A
mutant proviruses was severely restricted but was rescued by cotransfection with a wild-type Orf-A expression vector. In addition, virions derived from
orf-A
mutant proviruses expressed reduced infectivity for feline PBMC. Our findings suggest that Orf-A functions involve multiple steps of the FIV life cycle including both virion formation and infectivity. Furthermore, these observations suggest that Orf-A represents an FIV-encoded analog more similar to the accessory gene
vpr
,
vpu
, or
nef
than to the regulatory gene
tat
encoded by the primate lentiviruses.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology
Cited by
33 articles.
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