Figure 5.

Effect of HU treatment on replication factories in wild-type and cds1Δ cells. (A) Examples of the EGFP-PCNA distribution are shown above the graphs. In wild-type cells replication foci are maintained on HU and early S patterns accumulate after 2–4 h on HU. For each strain, >150 nuclei were scored. (B) As in panel A, but for the cds1Δ strain, in which we score the disassembly of replication factories in cells incubated on HU (cf. patterns at 0, 2 and 4 h of HU treatment). (C) Time-lapse imaging was performed on wild-type and cds1Δ fission yeast cells bearing EGFP-PCNA at 30°C. Cells were treated with incubated in 12 mM HU and 3D stacks were taken at 10 min intervals. Projections of individual frames are shown. Replication factories are lost by 1 h on HU in the cds1Δ mutant, while pattern progression proceeds in wild-type cells that had already entered S phase. A large fraction of the cells in an asynchronous population of fission yeast are in G₂ phase, and these accumulate in early S phase on 12 mM HU.