Control of DNA Synthesis in Amoeba proteus

Abstract

IT is important for our understanding of DNA replication to determine the part played by the cytoplasm in the initiation and maintenance of DNA synthesis in the cell. That cytoplasm can “switch on” DNA synthesis in cells which are in G₀ or G₁ has been clearly shown in studies of hybrid cells^1,2, in transfer experiments using Xenopus egg cytoplasm^3,4, and in nuclear transfer experiments using G₁ and S phases of the protozoan Stentor⁵. Whether the G₂ nucleus can be “switched on” without first undergoing mitosis is not certain—available evidence is conflicting^6–8. The following investigation was carried out on Amoeba proteus to determine (i) if S cytoplasm can initiate synthesis of DNA in the G₂ nucleus; (ii) if S cytoplasm can maintain synthesis of DNA indefinitely in “switched on” nuclei; and (iii) if G₂ cytoplasm can inhibit DNA synthesis in S nuclei.