In the above paper Fig. 1. The complete and correct bel 1 protein sequence of the human spumaretrovirus. Note that the corrected bel 1 protein has extensions at both the amino-and at the carboxy-terminus.

The human foamy virus (HFV) genome possesses three open reading frames (bel 1, 2, and 3) located between env and the 3' long terminal repeat. By analogy to other human retroviruses this region was selected as the most likely candidate to encode the viral transactivator. Results presented here confirmed this and showed further that a deletion introduced only into the bel1 open reading frume of a plasmid derived from an infectious molecular done of HFV abolished transactivation. In contrast, deletions in bel2 and bel 3 had only minor effects on the ability to transactivate. The role of the bel 1 genomic region as a transactivator was further investigated by eukaryotic expression of a genome fragment of HFV spanning the bel 1 open reading frame. A construct expressing bel 1 under control of a heterologous promoter was found to transactivate the HFV long terminal repeat in a dose-dependent fashion. Furthermore, it is shown that the U3 region of the HFV long terminal repeat is sufficient to respond to the HFV transactivator.

The nucleotide sequence of the human spumaretrovirus (HSRV) genome was determined. The 5' long terminal repeat region was analyzed by strong stop cDNA synthesis and S1 nuclease mapping. The length of the RU5 region was determined and found to be 346 nucleotides long. The 5' long terminal repeat is 1,123 base pairs long and is bound by an 18-base-pair primer-binding site complementary to the 3' end of mammalian lysine-1,2-specific tRNA. Open reading frames for gag and pol genes were identified. Surprisingly, the HSRV gag protein does not contain the cysteine motif of the nucleic acid-binding proteins found in and typical of all other retroviral gag proteins; instead the HSRV gag gene encodes a strongly basic protein reminiscent of those of hepatitis B virus and retrotransposons. The carboxy-terminal part of the HSRV gag gene products encodes a protease domain. The pol gene overlaps the gag gene and is postulated to be synthesized as a gag/pol precursor via translational frameshifting analogous to that of Rous sarcoma virus, with 7 nucleotides immediately upstream of the termination codons of gag conserved between the two viral genomes. The HSRV pol gene is 2,730 nucleotides long, and its deduced protein sequence is readily subdivided into three well-conserved domains, the reverse transcriptase, the RNase H, and the integrase. Although the degree of homology of the HSRV reverse transcriptase domain is highest to that of murine leukemia virus, the HSRV genomic organization is more similar to that of human and simian immunodeficiency viruses. The data justify classifying the spumaretroviruses as a third subfamily of Retroviridae.

We have identified the major immunogenic structural proteins of the human foamy virus (HFV), a distinct member of the foamy virus subfamily of Retroviridae.