FIG. 5.

Prolonged G₂ accumulation is correlated with the defective S-phase checkpoint but not the early G₂/M checkpoint. NBS1-LBI cells that had been stably infected with empty vector, wild-type Nbs1, or S343A Nbs1 were used in the various checkpoint assays. (A) Expression of transduced Nbs1 proteins assessed by immunoblotting. (B) Replicative DNA synthesis assessed 30 min after various doses of IR in the NBS1-LBI cell lines. (C) Quantitation of early G₂/M checkpoint data assessed by histone H3 phosphorylation in 293T cells transfected with empty vector or with kinase-dead ATM (293T+kdATM), an AT fibroblast cell line (GM5849), and the stable NBS cell lines. (D) Quantitation of percentage of total cells in G₂/M as a function of time after 6 Gy of IR in the isogenic NBS cell lines. All results are representative of at least three different experiment.