Reverse transcriptase and thymidine kinase as markers for tumorigenicity and viral contamination of cells

Continuous monitoring of enzymes, particularly those involved in nucleic acid synthesis could be a useful means of detecting infections and abnormalities in cells in culture. Model systems using mouse (3T3), human (MRC-5) and chick embryo cells infected with RNA tumour viruses were studied. Reverse transcriptase activities were determined by the incorporation of (3H) nucleotides into synthetic primer-templates or into complementary DNA of endogenous RNA and characterised by their specificity for primer-templates dT12-18.rAn, dG12-18.rCn, dT12-18.DAn and dG10.rCmn, their requirements for metal ions and inhibition by antisera. Measurement of reverse transcriptase is a more sensitive method than the COFAL test for the detection of RAV infection of chick cells. Iododeoxyuridine, bromodeoxyuridine and dexamethasone, which can induce latent C viruses, have no effect on MRC-5 cells; no increases in reverse transcriptase were detected and no C particles were seen by electron microscopy. Solid tumours developed in immunosuppressed mice injected s/c with 3T3 and MRC-5 cells chronically infected with MLV but none formed after injection of cells or virus suspension alone. Thymidine kinase activities of WI-38 and MRC-5 cells are greatly increased by infection with CMV or transformation with SV40. Mammalian tumours and tumour cell lines also show a high specific activity of cytoplasmic thymidine kinase.