Fig. 2. The cell cycle arrest caused by iron chelation is reversible. (A) HeLa cells were kept in 500 µM mimosine for 24 hours. Then, either mimosine was removed by replacing the medium (mimosine release, rel) or 1 mM FeSO4 (Fe) was added. Nuclei were prepared and their DNA content was analysed by flow cytometry at the indicated time points. The `0 h' control indicates a 24-hour treatment with mimosine only. (B) Proportion of cells in the G1, S or G2-M phases of the cell cycle at the indicated time points after release from mimosine-induced cell cycle arrest, as determined from the flow cytometry histograms shown in A. (C) In vitro replication assay of nuclei from the 0, 1, 2 and 4-hour samples from A. Nuclei were incubated in elongation buffer and the percentage of nuclei that incorporated labelled nucleotides is shown for each time point.