Abstract
T1 RNA fingerprints of the genomes of Akv-1 and Akv-2 C-type viruses are indistinguishable and oligonucleotide maps of these viruses are probably the same. Akv-1 and -2 share 55--75% of their large T1-resistant oligonucleotides with four MCF viruses isolated from AKR mice or from NIH Swiss mice that inherit either the Akv-1 or Akv-2 virus-inducing locus of AKR. The majority of Akv oligonucleotides missing from T1 fingerprints of MCFs and the majority of oligonucleotides unique to MCF viruses are clustered and lie at corresponding positions in the 3' half of the oligonucleotide maps of Akv and MCF viruses. The RNA sequences present in different MCF isolates but not present in Akv-viruses are related. These results are consistent with a recombinational origin of MCF viruses, as proposed by Hartley and Rowe and their collaborators.