Molecular organization of the chicken ets locus.

Chicken DNA segments homologous to the ets region from the transforming gene of avian erythroblastosis virus, E26, were molecularly cloned and shown to be almost identical to v-ets by sequence analysis. The transforming gene acids from two cell-derived sequences, myb and ets. Whereas the mammalian ets genes are present on two chromosomes, the chicken ets sequence is present as a single locus with v-ets homologous sequences found in nine regions over about 60 kb of genomic DNA. The major sequence difference between the v-ets and c-ets is found at the 3' end, resulting in different carboxy termini of p135 and the chicken proto-ets product. The chicken locus is primarily expressed in normal thymus cells as a 7.5-kb mRNA. The first two viral homologous regions are not found in this c-ets transcript or any other minor species, suggesting that they may not be true exons. Thus, the v-ets region of E26 demonstrates that two major structural differences may have occurred during the transduction of proto-ets sequences by the virus: (1) Truncation of sequences present at the 5' and 3' ends of the gene; and (2) Acquisition of noncoding proto-ets sequences into the virus. Either or both of these differences may be, in part, responsible for the oncogenic potential of this retrovirus.