A new variant of Rous sarcoma virus-33 nondefective, pathogenic for rats.

Rous sarcoma virus-33 (RSV-33) belongs to RSVs that have the least number of passages beyond its isolation from chicken tumor No. 1 among all current strains of RSV. Biological characterization indicated that it was pathogenic for rats.

Activated fos oncogene in rat embryo fibroblasts transformed by ras and myc oncogenes.

Rat embryo fibroblasts (REF) were transformed by simultaneous gene transfer of the complementary oncogenes ras and myc using the calcium phosphate coprecipitation method. Cell lines derived from transformation foci expressed in addition to ras and myc cellular oncogene fos while normal REF did not express ras, myc and fos according to the hybridization methods used. The transformed cell lines produced colonies in soft agar and tumors in newborn syngeneic rats.

BrdU-induced changes in the provirus of PR-RSV in mammalian cells.

Previously we demonstrated differences in the organization and methylation pattern of integrated Rous sarcoma proviral sequences in helper-dependent virogenic rat TWERC cells. In the present study we attempted to induce changes in the integrated viral genome of TWERC cells using 5-bromodeoxyuridine (BrdU). Four clones (A, B, C, and F) derived from the parental cell line were treated for 10 months with different concentrations of BrdU.

Detection of viral markers and incomplete viral genome rescue from ASV transformed rodent cells.

Two non-virogenic rat cell lines TWERC and FR transformed with PR-RSV and FSV, respectively, were analyzed. Both these cell lines contained vRNA, but only in TWERC cells was the major viral polypeptide p27 synthetized. Transforming virus can be rescued from both cell lines only after fusing them with chicken fibroblasts preinfected with avian leukosis viruses of subgroup A, C, D, F and both td mutants of PR-RSV-C and B77-C.

Virus-specific RNA in selected cell lines derived from RSV-induced tumour.

The presence of virus-specific RNA in mammalian tumour cell lines of RSV aetiology was studied using molecular hybridization between the PR-RSV 3H-DNA probe synthetized by the endogenous RNA-directed DNA polymerase reaction and cellular RNA. It was found that both virogenic XC cells harbouring the full PR-RSV genome and cryptovirogenic RVP3 cells harbouring an incomplete PR-RSV genome contain virus-specific RNA. The degree of homology between such RNA and PR-RSV 3H-DNA probe reached 10--12% in XC cells and 28--30% in RVP3 cells.