Multipotential hemopoietic cell lines isolated from stem cell cultures infected with Friend virus complex (MuLV + F-SFFV) show presence of MuLV but not F-SFFV.

The only factor-dependent or factor-independent hemopoietic murine stem cell lines which can be permanently maintained in vitro are cell lines which originate from bone marrow cultures of congenic mice differing in the Fv-2 locus infected with Friend spleen focus forming virus (F-SFFV) in conjunction with either Rauscher or Friend helper virus (R-MuLV or F-MuLV). We determined the viral state of these cells by restriction enzyme analysis, measurement of SFFV and MuLV related RNA, immunoprecipitation analysis of viral related proteins and biological activity to test whether integration and expression of R-MuLV or F-SFFV are obligatory. All stem cell lines (SUT, JUT, 416B) showed expression of MuLV coded proteins or virus but SFFV was not found in these cell lines. A two-fold difference of RNA hybridizing with SFFV-specific cDNAs observed in stem cells of Fv-2rr and of Fv-2ss genotype is in agreement with data published earlier.