An analysis of the recovery of Tetrahymena from effects of cycloheximide

When cycloheximide (0.2 μg per ml) was added to synchronized cultures of Tetrahymena pyriformis GL‐C, the initial rate of incorporation of 14 C‐leucine was reduced to about 20% of the rate observed in control cells. After one hour, the rate increased fairly abruptly to about 60% of the control rate. The cells in cycloheximide underwent synchronous division about three hours after addition of cycloheximide. A second addition of cycloheximide had little effect on either the rate of incorporation or on the time of cell division in the drug. The medium in which cells had recovered brought about full inhibition of 14 C‐leucine incorporation in fresh cells, indicating that recovery was not accompanied by appreciable degradation of the cycloheximide. It was therefore concluded that during recovery the cells were either adapting to the cycloheximide or excluding it. The recovery process shows some specificity, since cells which had recovered from cycloheximide, and had become insensitive to a second dose of this drug, still retained full sensitivity to another drug, colchicine. Conversely, cells recovering in colchicine became insensitive to fresh colchicine but remained sensitive to cycloheximide.