Alteration of ribonucleotide reductase in aphidicolin-resistant mutants of mouse FM3A cells with associated resistance to arabinosyladenine and arabinosylcytosine.

Aphidicolin-resistant mutants of mouse FM3A cells were isolated and characterized. Most of the mutants were of a type showing associated resistance to arabinosyladenine, arabinosylcytosine, deoxyadenosine, and excess thymidine. This phenotype could also be observed in a variant line selected by resistance to a low level of arabinosylcytosine. In cell-cell hybrids, aphidicolin resistance as well as this cross-resistance behaved a codominant traits. The mutants had an increased dATP pool and decreased ability to incorporate labeled deoxycytidine into macromolecules. Genetic and biochemical evidence suggested that the mutation conferring the pleiotropic phenotype resulted from a change in ribonucleotide reductase activity such that the enzyme was desensitized to the allosteric negative effector dATP. This alteration of the enzyme could account for the marked change in deoxynucleotide pools and for the aphidicolin resistance of the mutants.