Abstract
Addition of diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) to permeabilized G1-arrested baby hamster kidney cells resulted in the stimulation of DNA synthesis. No stimulation was observed in cells from exponentially growing cultures. The Ap4A-stimulated [3H]dTTP incorporation was inhibited by nalidixic acid, daunomycin, chloroquine diphosphate, EDTA, and N-ethylmaleimide. It was dose-dependent in regard to the amount of permeabilized cells and of Ap4A. Numerous replication eyes were formed in the DNA molecules of stimulated cells. Pulse-chase experiments showed that the synthesis of DNA was discontinuous, resulting in the appearance of approximately 4S Okazaki fragments and their ligation to high molecular weight DNA. These results strongly suggest that Ap4A stimulated the initiation of DNA synthesis in baby hamster kidney cells that had been arrested in G1 by serum deprival.