The Yeast Cell Cycle: Coordination of Growth and Division Rates

Changes in activities of several enzymes involved in carbohydrate metabolism during the cell cycle of Saccharomyces cerevisiae

“…The technical improvements described in Materials and Methods reduced the frequently observed tendency of the fractions containing the larger cells to be contaminated with small cells (10,13). As discussed by others (1, 6, 10), certain limitations inherent in the method prevent strict separation of the cells on the basis of size alone, i.e., to some extent the separation may have been the result of differences in cell shape and density.…”

“…Knowledge of possible variations in enzyme activities during the cell cycle is necessary to understand fully the metabolic behavior of the entire microbial culture. This requires methods to obtain subpopulations at defined stages of the cell cycle.In the past, the activity patterns of a variety of enzymes have been determined in synchronously dividing yeast cultures (10,27,28). However, as discussed by other investigators, many of these earlier results may have been flawed by technical artifacts, since the synchronization techniques that were used could cause serious perturbations in enzyme activity (6, 7,10,29).…”

“…However, as discussed by other investigators, many of these earlier results may have been flawed by technical artifacts, since the synchronization techniques that were used could cause serious perturbations in enzyme activity (6, 7,10,29). Creanor and Mitchison (7) developed a method of producing synchronous cultures of Saccharomyces cerevisiae by selection of small unbudded cells from an elutriator rotor, a method which appeared to reduce metabolic perturbations markedly.…”

Regulation of CDC9, the Saccharomyces cerevisiae gene that encodes DNA ligase.

“…Initial studies on the activities of various enzymes in cultures of synchronously dividing cells did show significant periodic fluctuations in activity (21). However, subsequent work which examined synthesis of over 200 major yeast proteins found no evidence for periodic synthesis; instead, the proteins analyzed showed exponential synthesis during the cell cycle (7). It was suggested that the previously observed activity modulations were the result not of changes in enzyme synthesis but rather of periodic changes in regulatory molecules affecting enzyme activity (8).…”

“…It was suggested that the previously observed activity modulations were the result not of changes in enzyme synthesis but rather of periodic changes in regulatory molecules affecting enzyme activity (8). The only exceptions noted were the histones; these proteins did show a cell cycle periodicity in synthesis, being synthesized maximally in early S phase (7). Expression of the yeast histone genes is now known to be cell cycle regulated by both transcriptional and posttranscriptional controls (10,13).…”