FIG. 5.

p53-dependent cell cycle arrest does not require Siah genes. (A) Asynchronously growing wild-type, Siah1a^−/−, Siah1b^−/Y, Siah2^−/−, or Siah2^−/− Siah1a^−/− MEFs were subjected to gamma irradiation (0 or 15 Gy). Cell cycle distributions were assessed 24 h after treatment by BrdU labeling and flow cytometry. The percentage of cells in each phase of the cell cycle (lower left, G₁; upper, S; lower right, G₂/M) is shown. Distributions shown are representative of duplicate determinations of each of two or more independent MEF preparations. (B) MEFs were harvested 24 h after gamma irradiation (5 or 15 Gy) or UV-C irradiation (60 J/m²) or after 48 h of culture in the presence of PALA (50 μM) and analyzed as described for panel A. The extent of G₁ cell cycle arrest is expressed as relative percent S phase, calculated by the following formula: (% BrdU positive in untreated cultures/% BrdU positive in treated cultures) × 100. The means ± standard deviations are derived from duplicate determinations of each of three independent MEF preparations of each genotype. Similar results were obtained in an independent experiment.