Association of Protein Phosphorylation and Cell Cycle Progression after X-irradiation of Two-cell Mouse Embryos

Summary

Studies of protein phosphorylation in the second cell cycle of mouse embryos were assessed by [³²P]-incorporation and one- and two-dimensional electrophoresis. Unirradiated and X-irradiated embryos were compared. X-irradiation in the G₂ phase led to a block in this cell cycle phase. The phosphorylation of proteins with molecular weights of 30 and 46 kDa specifically correlated with the G₂ phase–mitosis transition in normally dividing and in irradiated embryos. The time lag in the phosphorylation of these proteins between the unirradiated and X-irradiated embryos was identical to the duration of the radiation-induced G₂ block. X-irradiation immediately decreased the phosphorylation of a 29 kDa protein to below detectable levels. Re-phosphorylation of this protein preceded the following mitosis. It is suggested that the 29 kDa protein may be involved in the regulation of events that led to the radiation induced G₂ block and the initiation of mitosis after release.