FIG 4.

γH2AX colocalizes with the sites of active replication upon UV irradiation. (A) Cells were labeled with EdU prior to UV or NCS treatment. Images were contrast adjusted to visualize the foci clearly. (B) More than 70% of EdU foci colocalize with γH2AX foci. The colocalization is less than 3% for control and NCS-treated cells (inset). See Fig. S3 in the supplemental material for high-resolution images visualizing EdU and γH2AX foci colocalization. (C) γH2AX starts to accumulate at sites of active replication within a few minutes of UV exposure, as reflected in the percentage of EdU foci colocalizing with γH2AX foci. The colocalization peaks at around 30 min, after which it starts to go down. (D) Cells were labeled with EdU post-UV, right before fixation. As seen from more-or-less intact colocalization between EdU and γH2AX for the same time points as in panel C. γH2AX accumulation does not inhibit EdU incorporation altogether but slows it down (inset). The control populations in all the experiments were fixed right after EdU labeling. See also Fig. S4. Cells were irradiated with 10 J/m². Error bars are standard errors of the mean. Scale bars: 10 μm.