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Conditions necessary for the establishment and maintenance of transformation of human cells by wild type and temperature-sensitive mutants of SV40 were examined. For both early and late mutants, the frequency of transformation was found to be up to 5-fold higher, and virus yield 100-fold lower, at 39° than at 33°. No such effect was observed with the wild type virus under the same conditions. This observation is apparently at variance with previously published work, but may be explained by the semi-permissive nature of the cells that we used. Increasing the temperature to 40.5° caused cells transformed by the early mutant, tsA30, to lose T-antigen as detectable by staining, and also to lose the abilit to grow to high density, while it produced no effect on cells transformed by wild type virus.

The metabolism of adenosine and deoxyadenosine has been studied in Ehrlich ascites tumor cells and in a subline (EAC-R2) resistant to growth inhibition by 6-(methylmercapto)purine ribonucleoside (6MeMPR). The mutant cell line showed reduced rates of conversion of adenosine and deoxyadenosine into nucleotides. It was concluded from this that both compounds probably are phosphorylated by adenosine kinase. Comparison of the rates of nucleotide synthesis at increasing concentrations of adenosine indicated differences in the Km and Vmax values of the adenosine kinases in the parent and mutant strains. Competition experiments between adenosine and 6MeMPR showed that adenosine kinase in EAC-R2 had probably lost all affinity for the analogue. Selection for resistance to 6MeMPR therefore seems to have altered the structure of adenosine kinase, such that it has no activity with 6MeMPR and reduced activity with adenosine and deoxyadenosine.

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