The kinetics of RNA synthesis have been studied under various growth conditions using synchronized Tetrahymena pyriformis GL. The curves obtained are approximately linear in growth-supporting media but vary under other circumstances. The presence of amino acids in the medium stimulates RNA synthesis in Tetrahymem as it does in bacteria. Since these induced variations do not influence the essential features of the pre-cytokinetic period it is inferred that fluctuations in the rate of RNA synthesis described by others are probably not essential features of temperature-induced synchrony. In addition, the translational stability of division-related templates at syn- chronizing temperatures has been investigated. The synthesis of proteins necessary for cytokinesis is shown to be greatly reduced under conditions simulating a heat-shock. Inhibitor studies using cycloheximide indicate that protein synthesis is required longer into the cytokinetic phase than had previously been thought. Collectively the data are all compatible with the hypothesis that synthesis of division-related proteins is drastically reduced in heat-shocked Tetruhymena and that the basis for this reduction is hydrolysis of template RNA without concurrent translation.
We have recently demonstrated a striking temperature dependent decay of RNA in Tetrahymena (Byfield and Scherbaum, '66a), a ciliated protozoan that can be brought into division synchrony by temperature fluctuations (Scherbaum and Zeuthen, '54). In addition, evidence has been presented for a marked dependence on temperature of the protein synthesizing efficiency which we have defined as the amount of protein synthesized/average RNA template (Byfield and Scherbaum, '67b). These phenomena, taken together, suggest a possible mechanism for the induction of division synchrony in Tetrahymena. Previous work has shown that synthesis of both RNA (Lazarus, Levy and Scherbaum, '64) and protein (Rasmussen and Zeuthen, '62) is required if temperature synchronized Tetrahymena are to divide. However, it has been suggested by Rasmussen and Zeuthen that a heat shock administered in the recovery period (i.e. following the last heat shock but prior to division) could effectively prevent division at times later than inhibitors of protein synthesis. This led them to propose that heat may exert its effect by causing removal of required proteins, possibly through heat denaturation. Watanabe and Ikeda ('65a) reinforced this interpretation by presenting data which suggested a peak