The four C-terminal amino acids of the v-erbA polypeptide are encoded by an intronic sequence of the v-erbB oncogene.

The genome of avian erythroblastosis virus (AEV), a defective acute leukemia retrovirus, carries two distinct cell-derived oncogenes in the structure 5' delta gag-erbA-erbB-delta env3'. The nucleotide sequence of the v-erbA gene was recently reported. In order to determine the boundary between the two adjacent oncogenes, the sequence of the v-erbA/v-erbB junction of AEV was compared to that of a recombinant lambda phage containing a chicken cellular sequence representing the 5' part of c-erbB. The four C-terminal amino acids of v-erbA are in fact encoded by a c-erbB intron-derived sequence thus demonstrating that the virus acquired a truncated c-erbA gene. Furthermore the 7 to 10 amino acid residues upstream from the 4 C-terminal amino acids mentioned above appeared to be derived from env-related sequences. The splice acceptor site at the beginning of the only open reading frame for v-erbB is also present and functional in c-erbB when expressed to generate a truncated EGF (epidermal growth factor) receptor. Thus AEV joins a truncated erbA gene to a truncated erbB gene through env-derived sequences and intronic sequences from c-erbB.