REGULATION OF INITIATION OF DNA SYNTHESIS IN CHINESE HAMSTER CELLS II . Induction of DNA Synthesis and Cell Division by Isoleucine and Glutamine in GI-Arrested Cells in Suspension Culture

Suspension cultures of Chinese hamster cells (line CHO), which had stopped dividing and were arrested in GI following growth to high cell concentrations in F-10 medium, could be induced to reinitiate DNA synthesis and to divide in synchrony upon addition of the appropriate amounts of isoleucine and glutamine . Both amino acids were required to initiate resumption of cell-cycle traverse . Deficiencies in other amino acids contained in F-10 medium did not result in accumulation of cells in G1 , indicating a specific action produced by limiting quantities of isoleucine and glutamine . In the presence of sufficient glutamine, approximately 2 X 10-6 M isoleucine was required for all cells to initiate DNA synthesis in a population initially containing 1 .5 X 105 cells/ml . Under similar conditions, about 4 X 10s M isoleucine was required for all G I-arrested cells to progress through cell division . In contrast, I X 10 --4 M glutamine was necessary for maximum initiation of DNA synthesis in GI cells, along with sufficient isoleucine . A technique for rapid production of GI-arrested cells is described in which cells from an exponentially growing population placed in F-10 medium deficient in both isoleucine and glutamine or isoleucine alone accumulated in G1