Synchronization of DNA synthesis in Tetrahymena populations by temporary limitation of access to thymine compounds

Abstract

Tetrahymena pyriformis, amicronucleate strain GL, was grown exponentially in 2 % proteose peptone plus 0.1 % liver extract. The synthesis of DNA was inhibited fully and selectively by uridine (20 mM), or thymidine (2 mM). After a generation's time (3 h) synthesis was resumed at nearly normal rate. Cell divisions were not affected, so with these agents replication of DNA can be strongly inhibited without disturbing the forthcoming cell division. When combined, uridine and thymidine inhibit DNA synthesis less strongly than each agent separately. When uridine was combined with a folic acid analogue, 0.05 mM methotrexate (4-amino-N10-methyl-pteroylglutamic acid), both DNA synthesis and cell divisions were inhibited. DNA synthesis stopped quickly, but cell divisions continued until the system had emptied of cells in division stages, and in G2. Release of these inhibitions could be made with thymidine. When this agent was added to cells incubated with uridine plus methotrexate for nearly a generation's time, synchronous DNA synthesis occurred immediately, and synchronous cell division followed. © 1970.