ABSTRACT
Earlier studies have established that the average speed of a replication fork is two to three times slower in early S-phase than in late S-phase and that the intracellular 2′-deoxyribonucleoside 5′-triphosphate pools grow during S-phase. In this study, the effect of the exogenous 2′-deoxyribonucleoside 5′-triphosphate (dNTP) supply on the average replication speed in a synchronised population of human HeLa cells was tested. The speed of replication fork movement was measured on extended DNA fibers labelled with 2′-deoxythymidine analogues 5-chloro-2′-deoxyuridine and 5-iodo-2′-deoxyuridine. We show that the introduction of exogenous dNTPs accelerates the replication process at the beginning of DNA synthesis only. In late S-phase, the administration of additional dNTPs has no effect on the speed of replication forks. The availability of 2′-deoxynucleotides seems to be a rate-limiting factor for DNA replication during early S-phase.
