DNA synthesis during growth and synchronous differentiation of Naegleria

Naegleria gruberi amoebae were stimulated to differentiate synchronously into flagellates under growth conditions by lowering the temperature from 32 degrees C to 20.5 degrees C. In the presence of nutrient medium, flagellates will eventually revert to amoebae and resume growth. The time course of nuclear DNA synthesis, using a double thymidine isotope procedure, was determined for: (1) logarithmically growing amoebae, (2) differentiating cells, and (3) flagellates that were reverting to amoebae. DNA replication ceased 10 min. after the stimulation of differentiation, and began again during reversion. Neither de novo transcription nor translation appear to be required for the cessation of DNA replication during differentiation.