Effect of cycloheximide on maturation of replicative intermediates into high-molecular-weight DNA in Tetrahymena

Replicative intermediates of discrete size (approximately 41 S) are observed in the eukaryotic organism Tetrahymena pyriformis, when the organism is grown under defined physiological conditions. The intermediates (believed to represent replicons) are synthesized and accumulated over longer periods of time (less than 90 min), if the cells are treated with low concentrations of cycloheximide. Under these conditions the rate of total DNA synthesis is only slightly inhibited (less than 15%), while maturation of intermediate DNA into high-molecular-weight DNA is completely blocked (greater than 98%). Cycloheximide appears to inhibit the maturation process more specifically than other protein synthesis inhibitors. Studies of the accumulated intermediates on alkaline buoyant density gradients demonstrate that initiation of new putative replicons occurs during treatment with cycloheximide.