ISOLATION AND CHARACTERIZATION OF INFECTIOUS FULL-LENGTH 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 D NAs 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 cell-free supernatants. The presence of virus particl es, suggested by a typical cytopathic effect, was confirmed by electro n microscopy. These viruses were characterized at different levels of the replication cycle. The proviral genomes revealed a taf deletion co mparable to that previously described in the human foamy virus (HFV) b el1 gene. Analysis of viral RNAs revealed similar patterns of transcri pts for SFV6- and SFV7-infected cells, with predominant expression of accessory genes. Characteristic major viral polypeptides were identifi ed by radioimmunoprecipitation for both isolates. Sequences homologous to the gene encoding Taf and to a potential internal promoter were id entified in the infectious clones and subcloned into expression vector s. Their functional properties were tested by transfection assays, whi ch provided evidence for the presence of a Taf-dependent internal prom oter in both SFV6 and SFV7 isolates.