[Further study of spontaneous virus production using transplantable HEp-2 cells as a model].

Two maxima of optic density were observed at zones of gravity 1.27 g/ml and 1.15-1.16 g/ml by sedimentation equilibrium in sucrose gradient of cultural fluid, obtained from the transplantable cells of the HEP-2 strain and concentrated by ultracentrifugation. These fractions thus isolated were tested for presence of RNA- and DNA-dependent DNA-polymerase. The structures with the density of 1.15-1.16 g/ml were identified with the oncornaviruses on the basis of characteristics flotating density, presence of RNA-dependent DNA-polymerase. Analyses of products of RNA- and DNA-dependent polymerases reaction, flotating density of oncornaviral nucleotides in sucrose and CsCl gradients are presented. The optimal conditions for reverse-transcriptase reaction of virions of D type viruses are characterized.