Identification of nucleotide sequences which may encode the oncogenic capacity of avian retrovirus MC29

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Abstract
The retrovirus strain MC29 induces a variety of tumors in chickens, including myelocytomatosis and carcinomas of the kidney and liver. The virus also can transform cultures of embryonic avian macrophages and fibroblasts. The genome of MC29 virus was characterized and nucleotide sequences that may encode the oncogenic potential of the virus were identified. MC29 virus can replicate only with the assistance of a related helper virus. The defect in replication is apparently a consequence of a deletion in 1 or more viral genes: the haploid genome of the MC29 virus has a MW of approximately 1.7 .times. 106, but the genome of the helper virus MCAV has a MW of approximately 3.1 .times. 106. Although MC29 virus transforms fibroblasts in culture, its genome has no detectable homology with the gene src that is responsible for transformation of fibroblasts by avian sarcoma viruses. Radioactive single-stranded DNA complementary to nucleotide sequences present in the genome of MC29 virus but not in the genome of MCAV (cDNAMC29) were prepared. If they are contiguous, these sequences (approximately 1500 nucleotides) are sufficiently complex to encode at least 1 protein. Homologous sequences were not detectable in several strains of avian sarcoma viruses or in an endogenous virus of chickens. These and other reports show that MC29 virus may contain a previously unidentified gene(s) that is capable of transforming several distinct target cells. The evolutionary origins of this putative gene and its location on the viral genome can be explored with cDNAMC29.