The defective acute leukemia viruses avian myeloblastosis virus (AMV) and E26 virus each contain an inserted cellular sequence related to the same highly conserved cellular gene, proto-amv. The oncogenes of these two retroviruses differ from this cellular proto-oncogene in gene structure, transcript structure, and gene product. AMV (7,8).In leukemic myeloblasts, the AMV oncogene is expressed as a 2-kb spliced subgenomic mRNA (9, 10). In contrast, proto-amv is expressed as a 4-kb transcript in normal and certain neoplastic hematopoietic tissues (11,12). This protoamv mRNA contains both 5' and 3' genetic information not present in AMV (ref. 13; unpublished data). In addition to differing gene and transcript structure, differing protein products of the AMV oncogene and proto-oncogene have also been found (3, 4).By using three antisera raised against different synthetic peptides predicted from the amv open reading frame, a common 48,000 Mr protein was specifically identified as the AMV oncogene product, p48mY', in AMV-transformed leukemic myeloblasts (3). The same three antisera also specifically precipitated a 110,000 Mr candidate normal cellular homolog, p110Protoa'v, in hematopoietic tissues that express the 4-kb proto-amv message (3).As a first approach to analyzing the functions of the AMV oncogene product, we have determined its-intracellular location. In addition, we have determined the location of the putative transforming protein, p135sag8""I'ts, of the E26 leukemia virus, which contains an oncogene with both amv-related and -unrelated cellular sequences (ets) (14-17). Leghorn chicken embryos (Pacesetter, Anaheim, CA). All cells except for the RP-9 cell line were cultured as described (3). RP-9 was maintained in liquid culture in the same media but supplemented with 20%o heat-inactivated chicken serum and 10% fetal calf serum. Avian erythroblastosis virus (AEV) was kindly provided by P. Duesberg (Molecular Biology Laboratory, University of California, Berkeley). MATERIALS AND METHODSCell Labeling. 4265The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Total RNA was extracted from S. mansoni by homogenization in 4 M guanidine thiocyanate followed by centrifugation through cesium chloride. Poly A(+) RNA was isolated by oligo(dT)-cellulose chromatography. The recovered poly A(+) RNA was subsequently shown to stimulate protein synthesis in a cell-free, rabbit reticulocyte system. Among the translation products were polypeptides with molecular weights of 18, 20, 26, 39, 42, and 50 kilodaltons that were recognized by rabbit anti-schistosome-denuded body IgG. Human infection serum IgG precipitated polypeptides with molecular weights of 16, 18, 30, 35, 37, and 42 kilodaltons. These results identify several mRNA's that may provide useful templates for preparation of cDNA for eventual cloning or as probes in various related experiments.