Sites of recombination between the transforming gene of avian myeloblastosis virus and its helper virus.

The sites of recombination between the transforming gene of avian myeloblastosis virus (AMV) and its natural helper myeloblastosis-associated virus (MAV) have been determined. In AMV, the cellular sequence substituting for the viral envelope (env) gene gives rise to a different carboxyl terminus of the DNA polymerase. The 5'-recombination site coincides with the RNA splice acceptor site for the production of env mRNA in MAV-infected cells. The 3'-recombination site reveals that the last 11 amino acids including the termination codon are shared by the env protein and AMV transforming protein. The RNA splice acceptor site for the generation of subgenomic v-myb mRNA is located 84 nucleotides downstream from the 5'-recombination site. The AMV transforming protein consists of helper virus-related sequences at both of its amino and carboxyl termini, and all but 84 nucleotides of the cell-derived v-myb sequence. The comparison of MAV gp85 amino acid sequence with those of subgroups B, C, and E indicates that the MAV present in clone lambda 10A2-1 belongs to subgroup B. The high degree of homology among different avian retroviruses of the same subgroup indicates that the amino acid sequence of gp85 is important in determining the conformation of the envelope glycoprotein.