Fig. 5. Intact intra-S-phase checkpoint and G₂–M cell cycle arrest in the absence of Eme1. (A) The MMC-induced intra S-phase checkpoint is not affected in Eme1^–/– ES cells. The proportion of [³H]thymidine incorporation in untreated wild-type (black square) and Eme1^–/– (gray diamond) cells was set as 100%. The decreased proportion of [³H]thymidine incorporation following increasing doses of MMC treatments was similar for both wild-type and Eme1^–/– ES cells. (B) G₂–M checkpoint activation of wild-type and Eme1^–/– ES cells following MMC treatment. Wild-type (left panel) and Eme1^–/– (right panel) ES cells were subjected to 1 µg/ml of MMC for 1 h and returned to regular medium for 6, 12 and 24 h, following which time they were stained with propidium iodide and analyzed by FACS. Both genotypes displayed similar cell cycle profiles, with cells progressively accumulating in the G₂/M phase.