Isolation of complementary DNA unique to the genome of avian myeloblastosis virus (AMV)

Avian myeloblastosis virus (AMV) can transform avian cells of hemopoietic origin, such as bone marrow, embryonic yolk sac, and circulating macrophages. The AMV is defective in its replication and can only replicate in the presence of helper viruses. This defectiveness in replication is probably due to a deletion or substitution of nucleotide sequences in its genome. The AMV genome contains no sequences homologous to the src gene, which is responsible for the transforming function of the sarcoma viruses. We attempted to identify the AMV sequences that may contain sequences which are responsible for its transforming function. We isolated a complementary DNA (cDNA_AMV) that hybridized preferentially to the RNA of the transforming AMV but not to the RNA of the helper virus. Using this cDNA_AMV as a probe, we determined the size of the AMV genome to be 33–34 S with a molecular weight of 2.6 × 10⁶. A similar molecular weight estimation of the AMV genome size was obtained by methylmercury-agarose gel electrophoresis of AMV RNA. In AMV-producer myeloblasts we can detect about 6000–7000 copies per cell of AMV-specific RNA, whereas fewer than 2 copies per cell of AMV RNA are found in helper virus-infected cells. In AMV nonproducer myeloblasts, about 2000 copies of AMV-specific RNA are detected. Furthermore, we find that RNA of AMV NP myeloblasts can only hybridize to 55% of cDNA complementary to helper virus genome. In uninfected hemopoietic cells, e.g., bone marrow cells, about 20 copies per cell of AMV-specific RNA are present, whereas in uninfected chick embryo fibroblasts less than 1 copy per cell is found.