Evidence for nucleoside channeling in vivo: Deoxythymidine incorporation into rat liver dTTP and nuclear matrix DNA

Previous studies in prokaryotes and in eukaryotic cell lines have indicated the possible existence of more than one dTTP pool accessible to DNA synthesis. To investigate this possibility in eukaryotes invivo, the incorporation of [3H]deoxythymidine into nuclear matrix-attached DNA and intracellular dTTP was examined in regenerating rat liver. The labeling of matrix DNA reached a maximum after a 5 min pulse and then began to rapidly decrease. Conversely, [3H]deoxythymidine incorporation into dTTP began to increase after 5 min and peaked 10 min after injection. Since the peak specific activity for [3H]deoxythymidine incorporation into matrix DNA precedes that into dTTP, there seems to be channeling of exogenous thymidine directly to sites of DNA replication, bypassing existing nucleotide pools.