... through mechanisms like uncoupling between strands or helicase being blocked. In case of the replisome remained associated with the fork, some proteins such as the Rrm3 DNA helicase remove the impediments and then the DNA synthesis is restarted. However, if the replisome dissociates and the fork collapses, it will not be a problem in eukaryotes, as forks coming from adjoining replicons replace the collapsed forks. If the collapse occurs at sub-telomeric regions, where there are no other forks, the forks have to be restarted in order to complete the replication. The Activation of Replication Checkpoints When a fork is stalled, the uncoupling of the MCM helicase and polymerase activities, or between leading and lagging strands, cause the amounts of single-stranded DNA (ssDNA) coated by replication protein A (RPA) to be exposed, which results in checkpoint signalling. Once ssDNA goes above a certain level, the Mec1/ATR checkpoint kinase, engaged to stalled forks, gets ...

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