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Identification of a feline immunodeficiency virus gene which is essential for cell-free virus infectivity
K Tomonaga1, J Norimine, Y S Shin
1Department of Veterinary Microbiology, Faculty of Agriculture, University of Tokyo, Japan.
Abstract:
Feline immunodeficiency virus (FIV) contains at least three small open reading frames (ORFs) in the genome, in addition to the three structural genes. Two of these ORFs (putative vif and ORF-A) have unknown functions. Northern (RNA) blot analysis of mRNAs from an FIV-infected cell line showed that the putative-vif-specific mRNA was expressed as a 5.2-kb species. To examine the function of the putative vif gene, we constructed mutants carrying a deletion in either the vif-like gene or the rev gene from an infectious molecular clone of FIV. Although the vif mutant produced virion-associated reverse transcriptase at a normal level upon transfection, cell-free virus prepared from the transfected cells could not infect feline CD4+ cells. The infectivity of the vif mutant, however, was demonstrated in a coculture of the transfected cells and feline CD4+ cells. We conclude that FIV contains the vif gene, which is structurally and functionally similar to that of the primate lentiviruses.
Insights
The feline immunodeficiency virus (FIV) vif gene is crucial for viral infectivity in feline CD4+ cells. This study demonstrates its similarity to primate lentiviruses, impacting FIV research.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Feline immunodeficiency virus (FIV) possesses multiple open reading frames (ORFs) beyond its structural genes.
- The functions of two FIV ORFs, putative vif and ORF-A, remain largely uncharacterized.
- Previous research indicates the expression of a 5.2-kb mRNA specific to the putative vif gene in FIV-infected cells.
Purpose of the Study:
- To investigate the functional role of the putative vif gene in the FIV life cycle.
- To determine if the FIV vif gene is essential for viral infectivity.
- To compare the FIV vif gene's structure and function to primate lentiviral vif genes.
Main Methods:
- Construction of FIV mutants with deletions in the putative vif or rev genes using an infectious molecular clone.
- Northern (RNA) blot analysis to detect and characterize mRNA species, including the putative vif-specific mRNA.
- Transfection of cell lines with FIV mutants and assessment of viral infectivity using feline CD4+ cells and coculture assays.
Main Results:
- The vif mutant FIV produced normal levels of virion-associated reverse transcriptase upon transfection.
- Cell-free virus derived from cells transfected with the vif mutant failed to infect feline CD4+ cells.
- Infectivity of the vif mutant was restored when using a coculture system involving transfected cells and feline CD4+ cells.
Conclusions:
- The feline immunodeficiency virus (FIV) contains a vif gene that is essential for viral infectivity.
- The FIV vif gene plays a critical role in the infection of feline CD4+ cells.
- The identified FIV vif gene exhibits structural and functional similarities to the vif genes found in primate lentiviruses.