The effect of temperature shifts on the budding cycle of Saccharomyces cerevisiae

Abstract

1. 1. Inocula of yeast cultures, Saccharomyces cerevisiae strain 25.8, in the stationary phase were diluted with fresh medium and immediately exposed to a temperature cycle treatment lasting 6 hr. In each cycle the cells were kept at the optimum temperature (33 °C) for 25 min, followed by the temperature shock of 5 min at 49.5 °C. At the commencement of the treatment 90 per cent of the cells were single. After the elapse of 3 hr, however, the cells began to bud (only one bud per cell) and by the end of the treatment the buds had grown to the size of the parent. The result is the formation of paired, enlarged cells. 2. 2. These paired cells appear, cytologically speaking, to be blocked in the same stage of their development. However, upon release from the treatment they do not proceed synchronously to cleavage or budding, as, for example, paired cells produced by X-irradiation (2.85 Kr/hr) [28]. For convenience, we refer to the temperature induced paired cells as pseudosynchronized cells (P-S). The P-S cells show a lag period of three hours at the end of the treatment, followed by a gradually increasing budding and fission activity similar to freshly inoculated normal cells. 3. 3. Biochemical analyses were performed on three stages: the logarithmic phase (growth and division), stationary phase (negligible growth and division), and at the end of the heat treatment (P-S cells, growth without division). 4. 4. An almost 50 per cent reduction in the amounts of RNA, and DNA (per dry weight) was found in the P-S cells when compared to normal log cells. Acid soluble sulfhydryl increased (during the treatment) by about 40 per cent. However, the concentration of sulfhydryl in the stationary phase cells has tripled over the log cell values. The glycogen content was found to be rather constant. 5. 5. Acid soluble labile phosphates and polyphosphates (ppt. at pH 2.5 and 4.5) approximately double during the temperature treatment. Acid insoluble polyphosphates in the stationary phase cells are only about 2 3 of the amount found in the exponentially growing cells and could not be detected at all in the P-S cells. 6. 6. Sedimentation of ribosomal particles isolated from cells of the three stages was studied. One peak (80 S) was found in both stationary and P-S cells, but at a lower concentration in the former. A second ribosomal peak (60 S) was present in the log cells. 7. 7. Biochemical data are discussed in the light of the results reported on paired, enlarged yeast cells produced by irradiation and by chemical blocking agents.