Focus formation in rat fibroblasts exposed to a tumour promoter after transfer of polyoma plt and myc oncogenes.

The gene encoding the large-T protein of polyoma virus (plt), the E1A genes of adenoviruses, the viral myc gene (v-myc) or rearranged forms of the cellular c-myc gene confer on rat embryo fibroblast (REF) cells in primary culture a series of new properties ('immortality', reduced serum requirement and sensitivity to transformation by viral and activated cellular oncogenes) but do not induce the appearance of transformed foci. We now report that focus formation can be induced after transfer of these genes into either REF or established FR3T3 rat cells by subsequent exposure to the tumour promoter 12-O-tetradecanoylphorbol 13-acetate (TPA). Frequencies of transformation are in the same range as those usually observed for transformation with complete polyoma DNA or with a mixture of cloned myc and ras oncogenes.

Nucleolar ultrastructure and transcription of preribosomal RNA in Rous sarcoma virus-transformed chick embryo fibroblasts treated with alpha-amanitin.

Uninfected and Rous sarcoma virus (RSV)-transformed chick embryo fibroblasts (CEF) were exposed to various concentrations of alpha-amanitin for different lengths of time. At a concentration of 4 micrograms alpha-amanitin/ml, RSV-transformed cells were shown to maintain a normal rate of transcription of all classes of RNA, whereas in uninfected cells transcription was reduced to a very low level. These observations cannot be accounted for by a difference in the penetration rate of alpha-amanitin through the plasma membrane.

[Cellular contaminants and structural proteins of Rous sarcoma virus (RSV), studied by polyacrylamide gel electrophoresis].

The number of polypeptides in highly purified preparations of RSV, of two different subgroups, produced in culture, has been compared to the polypeptides present in the supernatant of uninfected cultures and processed in identical manner. The analysis of PAGE-SDS shows that from 13 to 18 polypeptides present in viral preparations may be cellular contaminants. Fewer contaminating polypeptides are found in the myeloblastosis virus purified from plasma of Chicken.