Tubulin synthesis during the synchronous cell cycle of Tetrahymena

The distribution of polyribosome material and the synthesis of tubulin was determined for division synchronized Tetrahymena. Cultures of Tetrahymena pyriformis GL were induced to divide synchronously by the one-heat-shock-per-generation technique. After seven heat shocks (at 34 degrees C for 30 min) spaced on generation time apart (157 min), the cells divided synchronously at 80 and 195 min after the end of the last heat shock (EH). Sucrose gradient analysis of polyribosomes demonstrates a progressive reduction in the relative amount of monosomes compared with the total amount of ribosomal material recovered during the period between EH and the first synchronous division. During the period between the first and second synchronous divisions the percentage of monosomes rises immediately after division and does not change after 120 min EH at which time it is indistinguishable from levels found in log growth cells. The specific activity of tubulin was determined throughout the first and second synchronous cell cycles. Tubulin synthesis was measured by labeling cells with L-[35S]methionine and determining the levels of radioactivity comigrating with purified tubulin. A comparison of the resulting electrophoretic patterns reveals a marked induction of tubulin synthesis during G2 of the first and second (free-running) synchronous cell cycle. At its peak, tubulin is synthesized to a point approximately 60% higher than levels observed during the initial part of S phase during the synchronous cell cycle. The results are discussed in reference to other morphological events that occur during the cell cycle and in reference to the regulation of tubulin synthesis.