Do synchronizing temperature shifts inhibit RNA synthesis in Tetrahymena pyriformis?

Synchronizing temperatures and rRNA metabolism in Tetrahymena pyriformis

1. In Tetrahymena pyriformis pre-rRNA is synthesized and efficiently processed and translocated into the cytoplasm at both a supraoptimal (34 degrees C) and a suboptimal (8 degrees C) synchronizing temperature. 2. At the heat shock temperature (34 degrees C) no substantial differences in the kinetics of the main intracellular events of rRNA-metabolism compared to the optimal growth temperature (28 degrees C) were found. 3. The high temperature, however, induces a strong retardation of uptake of [3H]adenosine into the cells and a reduction of the cellular ATP pool size. 4. At the cold shock temperature (8 degrees C) the rates of transcription and nucleocytoplasmic transport of rRNA as well as of nucleotide pool equilibration are reduced to a similar extent (25-30% of the optimal rates at 28 degrees C). 5. The results are discussed and compared with the effects of sub- and supraoptimal temperatures on rRNA synthesis and processing in mammalian cells.

Adenine nucleotide metabolism in heat-synchronized Tetrahymena

The metabolism of acid soluble adenine nucleotides in heat-synchronized Tetrahymena pyriformis GL has been studied. In addition, the effect of the synchronizing temperature (34 degrees C) on adenine nucleotide metabolism in heat-synchronized cells has been determined. In cells induced to divide synchronously through heat treatment (cyclic pulses of 34 degrees C for 30 min alternating with a 30 min recovery period at 28 degrees C) variations occurred in the levels of adenine nucleotides when samples of cells were analysed at the end of the last thermal period and at various time preceding the first synchronous cell division. The specific activities of the adenine nucleotides were found to be significantly higher during a pulse label period performed at the end of the last thermal period than at any time during the subsequent synchronous division cycle. The synchronizing temperature was found to partially deplete the intracellular stores at ATP in heat synchronized cells. This decrease was reversible with ATP levels recovering after 15 min of incubation at 28 degrees C. Fluctuations in the levels and specific activities of the adenine nucleotides are discussed in their relation to macromolecular synthesis and the cell cycle in Tetrahymena.