The friend spleen focus-forming virus (SFFV) genome: Fractionation and analysis of SFFV and helper virus-related sequences

Abstract

An in vitro mouse fibroblast culture system is described for the propagation of high titers of Friend spleen focus-forming virus (SFFV) and its helper lymphoid leukemia virus (LLV). Utilizing these tissue culture-derived virus preparations and SFFV nonproducer mouse and rat cell clones, the genome of Friend SFFV has been analyzed by molecular hybridization. The results of this analysis indicate that the SFFV genome consists of sequences homologous to a portion of its helper LLV and sequences which are unique to SFFV. This conclusion was reached as follows. First, hybridization of complementary DNA (cDNA) prepared from Friend virus complex containing an apparent excess of SFFV to LLV to either LLV or homologous (LLV, SFFV) RNA indicated that there are additional sequences unique to the SFFV genome. A cDNA complementary to these SFFV-specific sequences has been fractionated by hydroxylapatite chromatography and has been shown not to anneal to LLV RNA. Second, hybridization of cDNA made to LLV with LLV or (LLV, SFFV) RNA indicated the presence of two populations of LLV sequences differing in their relative frequencies in stocks of Friend virus complex (LLV and SFFV). It is suggested that the more abundant population of sequences represents those LLV sequences associated with both the LLV and SFFV genomes, while the less abundant population represents LLV-specific speuences. Third, analysis of viral RNA sequences present in several SFFV nonproducer cell clones demonstrated high levels of expression of a portion but not all of the LLV genome as well as sequences which are SFFV specific. Taken together, these results suggest that the SFFV genome consists of both unique sequences which presumably are involved in erythroleukemic transformation and sequences which are shared with its helper LLV.