FUNCTIONAL COMPARTMENTATION OF DCTP POOLS - PREFERENTIAL UTILIZATION OF SALVAGED DEOXYCYTIDINE FOR DNA-REPAIR IN HUMAN LYMPHOBLASTS

The utilization of dCTP derived from de nora synthesis through ribonucleotide reductase in exponentially growing CCRF-CEM cells was compared with the metabolic fate of dCTP produced by the salvage pathway, Exogenous dCyd was not effectively incorporated into replicating DNA; instead, dCTP derived from 1 ribonucleotide reductase (labeled by [5-H-3]Cyd) was the main precursor for that purpose, apparently because of functional compartmentation of the dCTP pool in these cells, Studies of the metabolic route of incorporation of exogenous [5-H-3]dCyd into DNA of growing CCRF-CEM cells demonstrated that it was mainly incorporated through the DNA repair pathway. Incorporation of [5-H-3]dCyd into DNA of synchronized cell populations was maximal in G(1) cells, whereas [H-3]dThd incorporation occurred predominantly in S phase cells, When cellular DNA was density labeled by incubation with BrdUrd, repaired DNA, which was less dense than replicated DNA, was preferentially labeled by [5-H-3]dCyd. In contrast, replicated DNA was labeled by both [H-3]dThd and [5-H-3]Cyd, The DNA-damaging agents methylmethanesulfonate, ultraviolet irradiation, and gamma-irradiation inhibited [H-3]dThd incorporation, whereas they stimulated the accumulation of [5-H-3]dCyd in DNA. Based on these results, we propose that the dCTP pool is functionally compartmentalized in growing CCRF-CEM cells, dCTP derived from the salvage pathway is utilized predominantly for DNA repair, whereas the de nova pathway supplies dCTP far DNA replication.