We have shown previously that a low concentration of tritiated
deoxyadenosine, i.e., 1 microCi/ml, selectively kills wild-type S49 murine
lymphoma cells. Mutant cells resistant to [3H]
deoxyadenosine lacked
adenosine kinase completely but retained a significant level of
deoxyadenosine phosphorylating activity. To study further the specificity of [3H]
deoxyadenosine selection,
lymphoma cell clones resistant to 15 microCi/ml [3H]
deoxyadenosine have been derived. The resistant line, S49-dA15, is also resistant to high levels of nonradioactive
deoxyadenosine and to
deoxyguanosine but remains sensitive to
thymidine. The
thymidine inhibition of the growth of the mutant, in contrast to that of the wild-type cells, cannot be prevented by
deoxycytidine. The mutant line lacks
deoxycytidine kinase that also phosphorylates
deoxyadenosine. In addition, the mutant cells excrete a large amount of
deoxycytidine into culture medium, consistent with a failure of salvage of the
nucleoside in the absence of an appropriate
kinase, i.e.,
deoxycytidine kinase. In contrast, a
deoxycytidine kinase-deficient cell line that was selected with
arabinosylcytosine does not excrete
deoxycytidine and contains high
deoxycytidine deaminase activity. [3H]
Deoxyadenosine can be used as a selective agent for specific selection of
deoxycytidine kinase-negative mutants.