Identification and preferential expression in thymic and bursal lymphocytes of a c-ets oncogene-encoded Mr 54,000 cytoplasmic protein.

The avian retrovirus E26 is unique among acute leukemia viruses in its ability to induce transformation of cells belonging to either the myeloid or erythroid lineage. The genome of E26 carries two oncogenes, v-myb and v-ets, that are derived from distinct cellular loci, c-myb and c-ets. We have constructed a plasmid vector that allows expression of part of the coding region of v-ets in a bacterial host. Antisera to the bacterially synthesized ets protein specifically precipitated the E26-encoded P135gag-myb-ets transforming protein. These antisera permitted us to identify a chicken c-ets-encoded protein of Mr 54,000 (P54c-ets) that shares 7 out of 10 of its major [35S]methionine-containing tryptic peptides with the v-ets-encoded domain of P135gag-myb-ets. Unlike P135gag-myb-ets and the Mr 75,000 translation product of c-myb (P75c-myb), which are nuclear proteins, P54c-ets was found to be predominantly cytoplasmic. P54c-ets is expressed at low levels in most cell lines and tissues tested, including bone marrow cells and circulating lymphocytes. P54c-ets, together with a minor but closely related Mr 56,000 protein, was found to be expressed at high levels in chicken thymocytes and bursal lymphocytes.