Linear synthesis of sucrase and phosphatases during the cell cycle of Schizosaccharomyces Pombe

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Abstract
The synthesis of sucrase, acid phosphatase and alkaline phosphatase has been followed in synchronous cultures of the fission yeast Schizosaccharomyces pombe prepared by gradient sedimentation. These three enzymes follow a linear pattern of synthesis through the cell cycle, with a doubling in rate at a ‘critical point’ about one-fifth of the way through the cycle. Sucrasecan be rapidly derepressed by lowering the glucose concentration in the medium. This has been used to measure the sucrase ‘potential’ or capacity to synthesize sucrase on derepression. The potential exists at all times in the cycle, and follows a stepwise pattern with a sharp rise at the critical point. These results suggest that the functional genome doubles at the critical point. Since, however, the period of DNA synthesis is nearly one-third of a cycle before this point, there must be an appreciable delay between chemical replication and functional replication of the genome. In this respect S. pombe, a eukaryotic cell, differs markedly from bacteria. Other physiological events take place near the critical point, and a tentative model is suggested of what may be happening at the chromosomal level. Experiments with cycloheximide indicate that there is a delay between the synthesis and the appearance of the active enzyme in the case of sucrase and alkaline phosphatase.