164 Pattern Formation the Dependence of DNA and Protein
164 Pattern formation The dependence of DNA and protein biosynthesis on cytoplasmic pH during the cell cycle in Dictyostelium discoideum Rob Aerts, Tony Durston and Wouter Moolenaar, Hubrecht Laboratory, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands We measured cytoplasmic pH in Dictyostelium discoideum under various conditions, using the digitonin null-point method (Rink, T. J., Tsien, R. Y., Pozzan, T. (1982) /. Cell Bioi, 95,189. In synchronised cell populations the cytoplasmic pH clearly fluctuates during the cell cycle. These fluctuations coincide with fluctuations in the rates of biosynthetic processes; the rates of DNA synthesis and protein synthesis show a sharp optimum in the cytoplasmic pH range 7-40 to 7-45. The cytoplasmic pH of Dictyostelium discoideum can be changed by certain weak acids and bases. The effect of ammonia is concentration dependent; a low concentration is able to increase cytoplasmic pH, high concentrations have the opposite effect. Artificial manipulation of cytoplasmic pH influences the rate of DNA and protein synthesis and shows the same correlation between these processes and cytoplasmic pH as mentioned above. On the other hand, if DNA synthesis is inhibited in synchronous populations of cells then the cell cycle fluctuations in cytoplasmic pH continue. The interrelation between cytoplasmic pH and DNA synthesis in Dictyostelium discoideum as revealed by the experiments summed up above corresponds strikingly to the relation between intracellular pH and DNA synthesis established in a taxonomically quite different system, namely lymphocytes of the mouse (Gerson, D. F., Kiefer, H., Eufe, W. (1982) Science 216,1009). That in Dictyostelium discoideum, on the one hand, artificial manipulation of cytoplasmic pH influences the rates of biosynthetic processes, and on the other hand, fluctuations in cytoplasmic pH continue after DNA synthesis inhibition suggests that the cytoplasmic pH may be a general regulator of the cell cycle.
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