The Relationship between Genomic RNAs of Polycythaemic Forms of Spleen Focus-forming Friend Virus and its Helper Virus

We have studied the relationship between Friend spleen focus-forming virus (SFFV) and its helper lymphoid leukaemia virus (LLV) by comparing RNase T1 fingerprints of genomic RNAs. Our data indicate that about 70% of the SFFV sequence is a perfect copy of parts of the helper genome. We conclude that our SFFV and LLV isolates have co-evolved very closely and that SFFV-specific sequences are not identical in different Friend virus isolates.

^† Present address: Department of Genetics, Free University, De Boelelaan 1087, 1007MC Amsterdam, The Netherlands.