Synthesis of DNA in human lymphocytes: possible control mechanism.

Partially purified, isolated nuclei from lymphocytes either stimulated or not stimulated by phytohemagglutinin can equally well synthesize DNA when [(3)H]dTTP is used as precursor. Studies of DNA polymerase activity in nuclei and cytoplasm from these cells showed that the enzyme can be detected in either stimulated or nonstimulated lymphocytes. In nonstimulated lymphocytes the uptake of thymidine is very low. The use of inhibitors such as cycloheximide, arbinosylcytosine, and actinomycin D showed that a parallel existed between thymidine uptake and DNA synthesis. All the conditions in which DNA synthesis was inhibited resulted also in an inhibition of thymidine uptake.