Avian nephroblastoma virus MAV-2(N) and avian osteopetrosis virus MAV-2(O) are genetically distinct.

Avian myeloblastosis virus consists of a mixture of a defective leukaemia virus and several non-defective associated avian leukosis viruses. The genomes of two of the associated avian leukosis viruses were examined in this study and were chosen because one of them, MAV-2(N), induces predominantly nephroblastoma, while the other, MAV-2(O), induces predominantly osteopetrosis. Competitive hybridization studies employing labelled virion RNA and DNA from normal and malignant tissue failed to demonstrate a difference the genomes. However, examination of ribonuclease T1-resistant oligonucleotide maps revealed that MAV-2(N) RNA had five oligonucleotide fragments which were not present in the MAV-2(O) genome. Poly(A) selection of the oligonucleotides at the 3' end of the genome showed that the fragments unique to MAV-2(N) were not present at this end of the genome. These results suggest that two viruses differing in oncogenic manifestation also differ in genome composition.