The ability of murine acute leukemia viruses to infect and transform mouse hematopoietic progenitor cells in vitro will be investigated. Specifically the ability of such viruses (eg. Friend leukemia virus, Rauscher leukemia virus) to transform erythroid progenitors in vitro and the interaction of the virus infection with the normal regulator of erythroid progenitor growth, erythropoietin, will be examined. The time course of induction of erythrocyte specific markers such as globin messenger RNA, spectrin, and glycophorin in the infected progenitors will be determined. As cells infected with the ammonia and polycythemia strains of Friend leukemia virus show different phenotypic expressions following transformation, they will be studied for differences in specific cellular proteins during culture. Also planned are studies to discern whether or not myeloid and/or megakaryocytic progenitors can be transformed in vitro by the acute leukemia viruses.