FIGURE 1.

Enrichment of cells in G₁ phase using mimosine. A and B, HeLa S3 cells treated for 24 h with 0.5 mm mimosine (A) and with 1 mm mimosine or 4 mm thymidine (B) were released for the indicated times and analyzed for DNA content by flow cytometry. Percentages of cells with G₁, S, and G₂/M DNA content are shown. The results (percent) represent the mean ± S.D. from three independent experiments. The shaded histograms represent DNA content of asynchronous cells. B, right panel, overlay histogram of cells treated with 1 mm mimosine (solid line) and 4 mm thymidine (dotted line). C, schematic depiction of the two synchronization methods. Cells were treated with 4 mm thymidine for 15 h, washed with PBS, and incubated in drug-free medium for 9 h. Then, cells were incubated for a further 15 h with 1 mm mimosine (i) or 4 mm thymidine (ii). D and E, cells were synchronized by treatment with Thy → Mimo or Thy → Thy, released for the indicated times, and analyzed for DNA content by flow cytometry. Right panel, overlay histogram of cells treated with Thy → Mimo (solid line) and Thy → Thy (dotted line). Shaded histograms represent DNA contents of asynchronous cells (D) or Thy → Mimo-synchronized cells (release 0 h) (E).