Feline immunodeficiency virus ORF-Ais required for virus particle formation and virus infectivity.
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.
Gemeniano
Malou C
MC
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA.
Sawai
Earl T
ET
Leutenegger
Christian M
CM
Sparger
Ellen E
EE
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D005814:Genes, Viral; D049452:Green Fluorescent Proteins; D016089:Immunodeficiency Virus, Feline / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D008164:Luminescent Proteins / Q000235:genetics; D016366:Open Reading Frames; D012333:RNA, Messenger / Q000235:genetics; D014771:Virion / Q000472:pathogenicity*; D014779:Virus Replication / Q000235:genetics
D017931:DNA Primers; D008164:Luminescent Proteins; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins