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Reports
DNA replication in early S phase pauses near newly activated origins
Rebecca A. Frum, Paul D. Chastain II, Pingping Qu, Stephanie M. Cohen and David G. Kaufman
volume 7 | issue 10
15 May 2008Pages: 1440 - 1448
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During the S phase of the cell cycle, the entire genome is replicated. There is a high level of orderliness to this process through the temporally and topologically coordinated activation of many replication origins situated along chromosomes. We investigated the program of replication from origins initiating in early S phase by labeling synchronized normal human fibroblasts (NHF1) with nucleotide analogs for various pulse times and measuring labeled tracks in combed DNA fibers. Our analysis showed that replication forks progress 9-35 kilobases from newly initiated origins, followed by a pause in synthesis before replication resumes. Pausing was not observed near origins that initiated in the middle of S phase. No evidence for pausing near origins was found at the beginning of the S phase in glioblastoma T98G cells. Treatment with the S phase checkpoint inhibitor caffeine abrogated pausing in NHF1 cells in early S phase. This suggests that pausing may comprise a novel aspect of the intra-S phase checkpoint pathway or a related new early S checkpoint. Further, it is possible that the loss of this regulatory process in cancer cells such as T98G could be a contributing factor in the genetic instability that typifies cancers.
Authors
Rebecca A. Frum
University of North Carolina at Chapel Hill; Chapel Hill, NC
Paul D. Chastain II
University of North Carolina at Chapel Hill; Chapel Hill, NC
Pingping Qu
University of North Carolina at Chapel Hill; Chapel Hill, NC
Stephanie M. Cohen
University of North Carolina at Chapel Hill; Chapel Hill, NC
David G. Kaufman
University of North Carolina at Chapel Hill; Chapel Hill, NC