[Viral genome integration with nuclear DNA in chronic viral infection]

A possibility of the integration of tick-borne encephalitis virus RNA in the host cell genome is studied under the condition of long-term chronic infection of HEp-2 cells. Molecular hybridization of viral RNA, labelled with 3H-uridine, and of DNA from intact and chronically infected cells was performed in 50% formamide with 0,4 M NaCl with subsequent investigation of the hybridization product by means of equilibrium centrifugation in CsSO4. 0,3 and 0,5 mg of DNA were used in hybridization experiments. It is shown that RNA obviously forms hybrids with DNA from chronically infected cells, whose density varied from 1,55 to 1,46 g/ml, depending on the proportion of RNA and DNA in the hybrids. When the amount of DNA increased, the number of DNA-RNA hybrids increased as well. It is concluded that in nuclear DNA of cells chronically infected with tick-borne encephalitis virus, there are DNA sites, homologous to viral RNA, which are absent in intact cells.