Recombination between viral and cellular sequences generates transforming sarcoma virus.

A series of sarcoma viruses has been obtained from tumors induced by transformation-defective (td) mutants of the Schmidt-Ruppin strain of Rous sarcoma virus, subgroup A (SR-A). The RNA sequences of these "recovered avian sarcoma viruses" (rASVs) were compared with those of td mutants and of SR-A by oligonucleotide fingerprinting. Of six sarcoma-specific oligonucleotides present in SR-A RNA, three to six were missing in the RNAs of the four td mutants examined. All six isolates of rASV examined have regained these six oligonucleotides. In addition, most rASV RNAs have three new oligonucleotides not present in the RNA either of td mutants or of SR-A. The newly obtained oligonucleotides are located between 800 and 2600 nucleotides from the 3' end of rASV RNA, which corresponds to the src region of SR-A RNA mapped previously. Furthermore, viral RNAs of two td mutants isolated from a clone of rASV lack most src-specific oligonucleotides, including the three new ones. No differences were found among RNAs of td, SR-A, and rASV in the regions outside of src. Our results indicate that RNA sequences that rASVs have acquired from cells in the process of conversion from td virus to transforming virus are mapped within the src region and segregate with the transforming function. Some of the sequences are new and some are identical with those in SR-A RNA.