Rate of macromolecular synthesis through the cell cycle of the yeast Saccharomyces cerevisiae.

Abstract

Centrifugal elutriation was used to separate cells of Saccharomyces cerevisiae in balanced exponential growth according to position in the cell cycle. Macromolecular synthesis was examined. DNA synthesis was found to be periodic, but RNA and protein synthesis showed an exponential increase in rate. Two-dimensional electrophoresis was used to determine the rate of synthesis of individual proteins, with 111 of the more abundant cellular proteins selected for analysis from among thq more than 1000 proteins that migrate in the system. All the extknined proteins showed an exponentially increasing rate of synthesis. The total amount of protein increases continuously throughout the cell cycle in bacteria and yeast (1). However, both periodic and continuous increases in the activities of a variety of enzymes from many species of prokaryotic and eukaryotic organisms have been reported (1-4). Four general patterns of activity increase through the cell cycle have been considered. The patterns of continuous increase can be subdivided into two types: (i) exponential increase and (ii) linear increase with a doubling in the rate at some point during the cell cycle. Additionally, patterns of periodic increase can be subdivided into: (iii) step patterns like that of DNA accumulation and (iv) patterns in which activity reaches a peak followed by inactivation or degradation of the enzyme.Despite the extensive literature on periodic changes in enzymatic activity, speculations on the periodic nature of the synthesis of individual enzymatic proteins have been viewed with skepticism for the following reasons:(i) The various researchers reporting on enzyme accumulation measured enzyme activity and not enzyme synthesis. Mitchison and Creanor (5) reported that there is a delay of 20% of the cell cycle in the yeast Schizosaccharomyces pombe between synthesis of the enzyme precursor and its activation. This indicates that increased enzyme activity is not necessarily synonymous with enzyme synthesis. Furthermore, because the activities of many enzymes are regulated by feedback mechanisms, the periodicity that many researchers reported may be due to periodic changes in the synthesis of regulatory molecules affecting enzyme activity and not enzyme synthesis.(ii) Many studies of periodic synthesis utilized synchronous cultures prepared by induction techniques that involve media changes. These methods might be expected to drastically affect the nature of periodic synthesis of enzymes during at least the first synchronous division cycle. Furthermore, a study in Schizosaccharomyces pombe (6) showed that when total protein was subdivided into small groups on one-dimensional sodium dodecyl sulfate gels, their synthesis was exponential. In addition, in Saccharomyces cerevtsiae, the synthesis of a well-defined class of proteins, the ribosomal proteins, is nonperiodic (ref. 7; unpublished data).In light of these problems, we decided to reexamine enzyme synthesis in S. cerevisiae. Our reexamination is based on two recent technical innovation...

The critical size is set at a single-cell level by growth rate to attain homeostasis and adaptation

“…cycle 37,42,50,51 , a discontinuous pattern of growth in volume should cause changes in cell density over the cell cycle, consistent with the fact that yeast cells reach a maximum density shortly after budding 52,53 . All these observations point to a discontinuous mode of volume growth during the cell cycle of budding yeast, a property that has been well established in the fission yeast Schizosaccharomyces pombe 44,45,54 and may also apply to mammalian cells 55 .…”

Selective benefits of damage partitioning in unicellular systems and its effects on aging

“…Therefore, in the present study we simulated between 5% and 35% degradation of total proteins within 1 generation. Protein and RNA syntheses in S. pombe have been shown to increase exponentially during the cell cycle (19), whereas volume increase is biphasic linear (20). The model has therefore been tested for both types of growth, yielding comparable results ( Fig.…”

Regulation of RAD54- and RAD52-lacZ gene fusions in Saccharomyces cerevisiae in response to DNA damage.

“…This result leads us to conclude that whatever the nature of the inducing signal, it too shows a dose-dependent response to DNA damage. Some yeast genes have been shown to be regulated during the mitotic cell cycle, e.g., CDC9 (26), although the vast majority do not show such regulation (11). It is possible that RAD54 shows this kind of regulation, because it is known that cells exposed to X-rays characteristically show a division delay during G2, after DNA replication.…”