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. Author manuscript; available in PMC: 2005 Oct 17.
Published in final edited form as: Science. 2001 Oct 5;294(5540):96–100. doi: 10.1126/science.1061724

Fig. 2.

Fig. 2

Once-per-cell-cycle genome duplication is independent of the positions or density of replication origins. (A) Duplication of DNA exactly once-per-cell division is achieved with two mutually exclusive periods of the cell cycle during which either pre-RCs can be assembled but replication cannot initiate or replication can initiate but pre-RCs cannot be assembled. Regardless of where pre-RCs assemble, DNA is completely replicated and cannot be re-replicated until after cell division. (B) The assembly of extraneous pre-RCs can ensure that the entire segment of DNA is replicated in a timely fashion, without the need for specific DNA sequences to optimize origin spacing. Any pre-RCs that do not initiate are destroyed by passage of the replication fork and so cannot re-initiate on the replicated strands.