Endogenous type C particles from rat embryo cells treated with 5-bromodeoxyuridine.

Summary Type C particles were released from secondary W/Fu rat embryo cell cultures following exposure to 10 -4 m 5-bromodeoxyuridine for 36 hr. The particles were first detected in culture fluids by electron microscopy and uridine- 3 H labeling 2 days after drug treatment. Maximal release of type C particles occurred between 8 and 10 days. All rat embryo cells treated with 5-bromodeoxyuridine eventually fluoresced against antiserum to antigens from 2 mouse leukemia viruses. Fewer than 1% of the analog-treated cells contained budding particles as judged from electron microscopy. The induced type C particles banded at buoyant densities of 1.16 to 1.18 g/ml in sucrose equilibrium gradients. Culture fluids from 5-bromodeoxyuridine-treated rat embryo cells contained DNA polymerase activity. The type C particles failed to transform mouse or rat cells in vitro and did not induce neoplasms in neonatal mice or rats. 5-bromodeoxyuridine-treated rat embryo cells were not tumorigenic when injected into syngeneic newborns.