SPECIFIC SELECTION OF DEOXYCYTIDINE KINASE MUTANTS WITH TRITIATED DEOXYADENOSINE

We have shown previously that a low concentration of tritiated deoxyad enosine, i.e., 1 mu Ci/ml, selectively kills wild-type S49 murine lymp homa cells. Mutant cells resistant to [H-3]deoxyadenosine lacked adeno sine kinase completely bur retained a significant level of deoxyadenos ine phosphorylating activity. To study further the specificity of [H-3 ]deoxyadenosine selection, lymphoma cell clones resistant to 15 mu Ci/ ml [H-3]deoxyadenosine have been derived. The resistant line, S49-dA15 , is also resistant to high levels of nonradioactive deoxyadenosine an d to deoxyguanosine but remains sensitive to thymidine. The thymidine inhibition of the growth of the mutant, in contrast to that of the wil d-type cells, cannot be prevented by deoxycytidine. The mutant line la cks deoxycytidine kinase that also phosphorylates deoxyadenosine. In a ddition 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 cona ast, a deoxycytidine kinase-deficient cell line that was selec ted with arabinosylcytosine does not excrete deoxycytidine and contain s high deoxycytidine deaminase activity. [3H]Deoxyadenosine can be use d as a selective agent for specific selection of deoxycytidine kinase- negative mutants.