Association of protein phosphorylation and cell cycle progression after X-irradiation of two-cell mouse embryos

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.