Abstract
Foamy viruses (FVs) are complex retroviruses which have been isolated from different animal species including nonhuman primates, cattle, and cats. Here, we report the isolation and characterization of a new FV isolated from blood samples of horses. Similar to other FVs, the equine foamy virus (EFV) exhibits a highly characteristic ultrastructure and induces syncytium formation and subsequent cell lysis on a large number of cell lines. Molecular cloning of EFV reveals that the general organization is that of other known FVs, whereas sequence similarity with its bovine FV counterpart is only 40%. Interestingly, EFV buds exclusively from the plasma membrane and not from the endoplasmic reticulum (ER), as previously shown for other FVs. The absence of the ER retrieval dilysine motif in EFV Env is likely responsible for this unexpected sorting pathway.
Highlights
Foamy viruses (FVs), known as spumaviruses, are widespread complex retroviruses which have been isolated from nonhuman primates, cattle, and cats
All FVs characterized to date have very large genomes with the classical gag, pol, and env structural genes and additional regulatory open reading frames (ORFs) located at the 3Ј end of the env gene which are under the control of both the 5Ј long terminal repeat (LTR) and an internal promoter (IP) [14]
All of these sera recognized in human foamy virus (HFV)-infected cells mainly the HFV 130-kDa Env precursor as well as a higher-molecular-weight band recently defined as the 160-kDa Env-Bet fusion glycoprotein (Fig. 1) [4, 11]
Summary
Foamy viruses (FVs), known as spumaviruses, are widespread complex retroviruses which have been isolated from nonhuman primates, cattle, and cats. Recent findings regarding FVs raise important issues of general interest Some of their features, such as the formation of a specific pol mRNA and the infectivity of the incoming viral DNA contained in extracellular virions [26, 28], set FVs apart from all other retroviruses. The ultrastructure of the extracellular virion and the genomic organization were investigated and compared to those of other cloned FVs. displaying limited sequence similarities with primate FVs, EFV is phylogenetically closer to nonprimate FVs, especially to the bovine foamy virus (BFV). In contrast to other known FVs, EFV buds exclusively from the plasma membrane
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