Synchronization of cell division inTetrahymena pyriformis by a repetitive temperature cycle

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.

Growth and cloning of Tetrahymena pyriformis on solid meduium

A method of obtaining clones of Tetrahymena pyriformis on solid medium has been developed. The medium consists of a basal layer of 1.5% agar topped with 2 ml of 0.3% agar in sterile, plastic petri plates (100 by 15 mm). Both agar layers contain either 2% proteose peptone and 0.1% liver extract (complex medium) or defined medium supplemented with proteose peptone. After drying, 0.5 ml of liquid culture is spread evenly over the top agar, and the plates are then sprinkled lightly and evenly with autoclaved dry Sephadex G-25 (fine). Cell colonies can be observed after 5 days of incubation either by viewing with a microscope or without the aid of a microscope after staining. Plating efficiency is high on either complex or defined medium with a number of strains of Tetrahymena, both micronucleate and amicronucleate. Colonies can be picked and transferred to liquid culture for further growth. The existence of clones was demonstrated by plating a mixture of two different drug-resistant mutants. The method should prove useful in selective procedures for the isolation of mutants and for determining survival after treatments such as ultraviolet irradiation.

Studies of native glycogen isolated from synchronized Tetrahymena pyriformis (HSM)

Native glycogen was isolated from Tetrahymena pyriformis (HSM) by isopycnic centrifugation in cesium chloride density gradients. A density of 1.62 to 1.65 was isopycnic for glycogen. Most of the banded glycogen existed as 35 to 40 mmicro particles which had a sedimentation coefficient of 214. These particles were composed of aggregates of 2 to 3 mmicro spherical particles. Extraction of glycogen with hot alkali reduced the sedimentation coefficient of native glycogen from 214 to 64.7 and the particle diameter from approximately 40 to 20 mmicro and smaller. Cell division was synchronized by a repetitive 12-hour temperature cycle, and glycogen was measured at several times during the cell cycle. The temperature cycle consisted of 9.5 hours at 12 degrees C and 2.5 hours at 27 degrees C. Approximately 90 per cent of the cells divided during the last 1.5 hours of the warm period. The carbohydrate/protein ratio of cells at the end of the cold period was 0.27 and was reduced slightly during the warm period. Glucose was incorporated into glycogen during both periods, although the rate of incorporation was greater during the warm period. No preferential incorporation on the basis of particle size was noted. Incorporation was measured in both native glycogen and KOH-extracted glycogen. Tetrahymena glycogen is compared with rat liver glycogen previously isolated by similar procedures, and the significance of using combined rate-zonal and isopycnic centrifugation for isolating native glycogen is discussed.