Radiation-enhanced murine sarcoma virus genome rescue activity.

Although the doses of X-ray (312-2,500 R) used for irradiation of cells caused impairment of DNA synthesis and cell replication, co-cultivation of X-irradiated MuLV- carrier cells with un-irradiated nonproducer cells of MSV-induced tumour resulted in as much as 20-fold increase in MSV retrieval compared with the un-irradiated control. The enhancement was apparent also as a 3-fold increase in the number of cells producing MSV (infectious centers) in the co-cultivation plate. This suggested that the MSV genome rescue efficiency in terms of MSV per cell, as well as the number of cells producing MSV, increased markedly. By uridine-3H-labeling and focus assay experiments, evidence was presented which suggested that an increase in MSV/MuLV ratio in the culture fluid of co-cultivation plates was obtained when the MuLV-carrier cells were pre-irradiated. By contrast, X-irradiation of the nonproducer cells prior to co-cultivation caused only reductions of MSV genome rescue efficiency. However, use of X-irradiated MuLV-carrier cells for co-cultivation with X-irradiated nonproducer cells restored this efficiency to some extent. The dose-survival curve of the nonproducer cells was not much different from those of the MuLV-carrier cells after X-irradiation. It was suggested that the viability of nonproducer cells was required for replication of MuLV transferred from the carrier cells and for subsequent MSV genome rescue.