INCREASE IN MACROMOLECULAR AMOUNTS DURING THE CELL CYCLE OF TETRAHYMENA: A CONTRIBUTION TO CELL CYCLE CONTROL*

Increases in RNA, protein and cell size were determined cytophotometrically during the cell division cycle of Tetrahymena. For these parameters different patterns were found. RNA accu-mulates slowly during Gi period and faster during macronuclear S. This agrees with the changing uridine incorporation rate which is at least partly related to the varying macronuclear DNA amount. Increases in protein content and cell size occur mainly during Gx and G2. This pattern was confirmed by determining the RNA: protein ratio in individual cells. It is minimal at the end of the G, period. These findings and evidence from the literature suggest that ini-tiation of DNA replication is under negative control by the relative RNA content of the cell