Occurrence of partial deletion and substitution of the src gene in the RNA genome of avian sarcoma virus

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Abstract
The genome size of 20 transformation-defective (td) viruses derived from different strains of Rous sarcoma viruses [Prague (subgroups A and C), Schmidt-Ruppin (subgroups A and D) (SR-D), Bratislava 77 and Carr-Zilber (subgroup D)] was examined by polyacrylamide gel electrophoresis [PAGE]. All of the td viruses except td SR-D have 35S RNA of the same size, i.e., class b RNA. Two of 5 td SR-D viruses examined have a slightly larger RNA, corresponding to a td deletion that is about 25% smaller than that of class b RNA. The RNase T1-oligonucleotide fingerprints of all the td SR-D viruses are identical, lacking 2 sarcoma-specific oligonucleotides. The fingerprints of these viruses also showed a minor oligonucleotide present at very low concentration. A study of heteroduplex molecules formed between genome-length c[complementary]DNA made from wild-type SR-D and 35S RNA of td SR-D showed a deletion loop of 2.0 and 1.5 kilobases [kb], respectively, at the map position of the src gene for these 2 classes of td SR-D viruses, confirming the results of PAGE. Some heteroduplex molecules with a substitution loop of 0.6-0.7 kb at the same site as the deletion loop were observed in all 5 of the td SR-D viruses. Apparently some of the td SR-D viruses have a partially deleted src gene and all of the td SR-D viruses have incorporated heterologous sequences of distinct length in some RNA molecules at the position of the src gene. The nature and origin of these heterologous sequences are discussed.