Figure 4

CDK1 phosphorylation is maintained in CHK1-depleted HCT116 cells during DNA replication stress. Western blot analysis of indicated S-phase regulatory proteins from extracts of HCT116 or HCT116 p53−/− cells pretreated with CHK1 or control siRNAs and exposed or not exposed to thymidine (2 mM, 24 h). β-Actin levels are presented as loading controls