Table 1.

Published evidence for and against a function for the replication checkpoint in regulating replisome stability

Evidence the replication checkpoint DOES regulate replisome stability	Evidence the replication checkpoint DOES NOT regulate replisome stability
ChIP data in S. cerevisiae
DNA polymerase subunits and RPA are reduced in abundance near an early firing origin in mec1Δ cells treated with HU. In contrast, the MCM helicase but not the polymerases are dissociated from the forks in rad53Δ cells [17, 49].	The replisome including polymerase and helicase subunits remains stable and associated with forks throughout the genome in HU-treated mec1Δ or rad53Δ budding yeast cells [18].
Polα and ε subunits are decreased in abundance near the early origin ARS305 in rad53 mutants and Polδ is lost at later times after HU treatment [50].	Polα and Cdc45 are retained near the early ARS305 origin in a rad53 mutant strain treated with HU even though they also start associating with a late origin[98]. Similarly, inactivation of the checkpoint using dpb11-1 or rad53 mutants did not cause loss of Polε from ARS305 in HU-treated cells [99].
Cdc45 is much less abundant near the early origin ARS305 in HU-treated mec1Δtel1Δ cells than in controls [51].	Replisome subunits remain associated with stalled forks induced by a protein-based replication fork barrier even when the checkpoint is inactivated by mec1 or rad53 deletion [100]
	Examination of PCNA abundance on leading vs. lagging strand in HU treated cells showed that the checkpoint actually promotes PCNA unloading from the lagging strand [55].
Other yeast data
When monitored by 2D gel electrophoresis of replication intermediates, the aberrant fork structures in rad53 mutant cells look the same as the structures caused by inactivation of replisome proteins [39].	S. pombe cds1Δ cells treated with HU retain the ability to synthesize DNA, and the ssDNA accumulated in these circumstances is dependent on MCM activity suggesting the helicase remains associated with the fork [101].
Checkpoint-deficient fission yeast show decreased PCNA staining in early replication patterns and increased PCNA staining in late patterns [43]	MMS-treated S. cerevisiae rad53Δexo1Δ double mutants retain functional forks that are capable of continuing DNA synthesis indicating the replisome may remain stable [102].
Xenopus extract replication data
In Xenopus extracts, Polε dissociates from chromatin when replication proceeds in the presence of CPT. The ATM/ATR kinases are needed for polymerase reloading in this circumstance [45].	Polε did not dissociate from the replicating Xenopus chromatin in response to aphidicolin treatment in checkpoint-deficient extracts [45].
When fork collapse was triggered by direct induction of a replication-associated double-strand break using a nuclease in the Xenopus extracts, the GINS subunits of the replicative helicase were lost from chromatin[53]. Polε was also lost in this system but MCM2-7, CDC45, and POLα were not.
Human and mouse cell data
The total amount of PCNA, POLE, POLD2, and CDC45 associated with chromatin is reduced in ATR-deficient cells treated with aphidicolin compared to control cells [54]. The level of MCM3 on chromatin was not changed.
Checkpoint-deficient human cells show decreased PCNA staining in early replication patterns and increased PCNA staining in late patterns [52]