RESUMO
The genome of the Friend strain of the spleen focus-forming virus (SFFV) has been analyzed by molecular hybridization. SFFV is composed of genetic sequences homologous to Friend type C helper virus (F-MuLV) and SFFV-specific sequences not present in F-MuLV. These SFFV-specific sequences are present in both the Friend and Rauscher strains of murine erythroleukemia virus. The SFFV-specific sequences are partially homologous to three separate strains of mouse xenotropic virus but not to several cloned mouse ecotropic viruses. Thus, the Friend strain of SFFV appears to be a recombinant between a portion of the F-MuLV genome and RNA sequences that are highly related to murine xenotropic viruses. The implications of the acquisition of the xenotropic virus-related sequences are discussed in relation to the leukemogenicity of SFFV, and a model for the pathogenicity of other murine leukemia-inducing viruses is proposed.
