Isolation and characterization of infectious fulllength DNA clones of chimpanzee foamy viruses SFV6 and SFV7: Evidence for a Taf-dependent internal promoter

We have cloned complete viral genomes directly from Hirt supernatant DNAs of simian foamy virus types 6 and 7 (SFV6 and SFV7) -infected cells. These clones were shown to be infectious by transfection into cells and subsequent infection of susceptible cells either by cocultivation or by passage of cellfree supernatants. The presence of virus particles, suggested by a typical cytopathic effect, was confirmed by electron microscopy. These viruses were characterized at different levels of the replication cycle. The proviral genomes revealed a taf deletion comparable to that previously described in the human foamy virus (HFV) bel 1 gene. Analysis of viral RNAs revealed similar patterns of transcripts for SFV6- and SFV7-infected cells, with predominant expression of accessory genes. Characteristic major viral polypeptides were identified by radioimmunopreciprtation for both isolates. Sequences homologous to the gene encoding Taf and to a potential internal promoter were identified in the infectious clones and subcloned into expression vectors. Their functional properties were tested by transfection assays, which provided evidence for the presence of a Taf-dependent internal promoter in both SFV6 and SFV7 isolates.