Abstract
The virion RNA of avian myelocytoma virus MC29 was hybridized to full genome length DNA of the Prague strain of Rous sarcoma virus and analyzed by heteroduplex mapping in the electron microscopy. The results show that MC29 specific sequences for which there are no homologous counterparts in the Rous sarcoma virus genome make up a contiguous stretch of RNA about 1.8 kilobases long. These sequences are located approximately in the middle of the genome, replacing the 3' half of the gag gene, the entire pol gene, and the 5' portion of the env gene, which are absent from MC29. This MC29 specific genetic substitution may contain information for the leukemogenic transformation of the host cell.