Ts mutants of E26 leukemia virus allow transformed myeloblasts, but not erythroblasts or fibroblasts, to differentiate at the nonpermissive temperature.

The myb, ets-containing avian acute leukemia virus E26 transforms myeloblasts, erythroblasts, and fibroblasts in culture and causes a mixed erythroid/myeloid leukemia in chicks. We report the isolation and characterization of four E26 mutants that are temperature-sensitive (ts) for myeloblast transformation. At the permissive temperature, tsE26-transformed myeloid cells resemble macrophage precursors and proliferate rapidly, provided the growth medium contains chicken myelomonocytic growth factor (cMGF). When shifted to the nonpermissive temperature the cells stop growing and differentiate into macrophage-like cells, as determined by their expression of morphological, functional, and antigenic markers of normal macrophages. They also lose their responsiveness to cMGF and secrete a cMGF-like factor. Ts mutants of E26 retain their leukemogenicity and their ability to transform both erythroblasts and fibroblasts at the nonpermissive temperature, suggesting that the myb oncogene of E26 causes myeloblast transformation and that ets is responsible for erythroblast and fibroblast transformation.