Division In Yeast Research Articles

Correlation of Glutamine Synthetase Activity with Cell Magnesium Concentration during Cell Division in Yeast Synchronized by Induction

Synchronization of cell division in the fission yeast Schizosaccharomyces pombe and the budding yeast Kluyveromyces fragilis was achieved by induction using the DNA synthesis inhibitor 2′-deoxyadenosine and by a magnesium-exhaustion technique. The activity of glutamine synthetase in these synchronized cultures oscillated. Variations in the intracellular magnesium concentration were also observed, and peaks in magnesium concentration correlated with peaks in enzyme activity. We suggest that the enzyme from yeast is unstable and that its activity is regulated in vivo by changes in the intracellular concentration of magnesium.

Cell size and cell division in yeast cultured at different growth rates

Cell size and cell division in yeast cultured at different growth rates

Genetic control of cell division in yeast cultured at different growth rates

HARTWELL et al.1,2 have isolated a number of temperature-sensitive mutants blocked at various stages of the cell division cycle of Saccharomyces cerevisiae. A characteristic feature of any temperature-sensitive cell cycle mutant is its execution point in the cell cycle, that is, the point in the cycle after which cells when shifted to the restrictive temperature undergo one further cell division. If cells are shifted to the restrictive temperature before the execution point, they are unable at the elevated temperature to complete any cell division. The execution point for a particular mutant is taken to be the stage in the cycle that the defective gene completes its function. The execution point of mutant strain cdc28 is at an earlier stage in the cycle than other cell cycle mutants3. Detailed investigations of a number of cell cycle mutants have suggested that the events in early G1 that culminate in the execution of the cdc28-mediated step represent ‘start’. There is evidence that passing ‘start’ in the cycle represents a point of commitment to division. Before the execution of the cdc28-mediated step, ‘start’, yeast is capable of several developmental programmes but after this step it is committed to the mitotic cell cycle2. We report here that at generation times varying from 2.1–6.18 h ‘start’ occurs approximately 2h before division. At slower growth rates the length of time from ‘start’ to division increases somewhat. These results are similar to the finding in the bacterium Escherichia coli that the time from the initiation of DNA synthesis to cell division is independent of growth rate except at slow growth rates4.

Genetic control of cell size at cell division in yeast

A temperature-sensitive mutant strain of the fission yeast Schizosaccharomyces pombe has been isolated which divides at half the size of the wild type. Study of this strain suggests that there is a cell size control over DNA synthesis and a second control acting on nuclear division.

Control of cell division in yeast using the ionophore, A23187 with calcium and magnesium.

A23187 is an ionophore which exhibits specificity for divalent cations and promotes their passive transport across biological membranes1. It therefore effects equilibration of divalent ions between the cell sap and the surrounding medium and counteracts any active accumulation of ions within the cell. Evidence, mainly from studies on sea urchin eggs, supports the hypothesis that calcium ions play an important part in bringing about cell division2–4. We have found that division in the fission yeast, Schizosaccharomyces pombe, is associated with a doubling in magnesium concentration within the cells5. It, therefore, seems likely that, if accumulation of divalent ions within the cell were an essential prerequisite of cell division, this should be inhibited by A23187 and cell division should not take place, and so we have investigated this possibility.

The biogenesis of mitochondria 26. Mitochondrial recombination: the segregation of parental and recombinant mitochondrial genotypes during vegetative division of yeast.

The vegetative segregation of parental and recombinant mitochondrial (cytoplasmic) genomes of Saccharomyces cerevisiae were compared by experiments involving the micromanipulation of early zygotic buds. Recombinant mitochondrial genomes are formed rapidly upon zygote formation and initial zygote buds are frequently composed of varying proportions of recombinant and parental type gnomes, which then all segregate in a similar fashion. Evidence suggesting that some formation of recombinant genomes can continue in the early zygote progeny is presented, but the possibility that recombination is restricted to the zygote has not been excluded. Polarity phenomena appear to be determined by the mechanism of the mitochondrial recombination events rather than by the mechanism of distribution of recombinant genomes to zygote progeny.

SACCHAROMYCES VAFER AND S. INCONSPICUUS SPP.N.

During the re-examination of cultures deposited with the Yeast Division of the Centraalbureau voor Schimmelcultures, Delft, representatives of two hitherto undescribed species of the genusSaccharomyces were encountered.

Radioprotection by p-Chloromercuribenzoate of Haploid, Diploid, and Tetraploid Yeast

The notion that damage to the sulfhydryl groups of the cell is responsible, at least in part, for the lethal effects of ionizing radiation has persisted for many years despite evidence that other types of damage may be more important. A point often overlooked is that the formation and stability of the mitotic, or spindle, apparatus depends on the maintenance intact of the sulfhydryl groups of certain proteins (1). Damage to these proteins may well be as effective in causing division delay or inhibition as damage to DNA. The involvement of sulfhydryl groups in the yeast division process is suggested by the finding that the addition of cysteine to a filamentous yeast mutant causes it to divide normally (2). Although sulfhydryl compounds, such as cysteine and cysteamine, have been used extensively for radiation protection in many organisms and may function by forming mixed disulfides with proteins within the cell (3), a very few attmpts have been made to use specific, reversible sulfhydryl inhibitors to protect the sulfhydryl groups of the cell during irradiation. Barron (4) used p-chloromercuribenzoate (p-CMB), a specific sulfhydryl reagent, to mask the sulfhydryl groups of the enzyme urease. This masking procedure protected urease from a y-ray dose of 200 r. Patt (5) injected mice with p-CMB but did not obtain protection. The studies reported here were initiated (6) in an attempt to demonstrate in vivo protection of yeast by p-CMB.

Timing of enzyme synthesis during synchronous division in yeast

Timing of enzyme synthesis during synchronous division in yeast

An x‐ray induced block preventing cell degeneration and accompanying an inhibition of cell division in yeast

Growing yeast cells given a low dose of x radiation adequate to inhibit cell division were found after a period of starvation to be more viable and also more capable of taking up P/sup 32/ and oxygen and producing carbon dioxide than were unirradiated cells. The possibility was discussed that the action of radiation was somehow to stabilize the cell membrane or a component structure and thus preserve these capacities through the period of starvation, as well as prevent a loss of phosphorus and nitrogen compounds such as occurred from unirradiated cells. The starvation responses occurred in young cells, but not in old cells. In addition, a reduced potassium retentivity and rate of endogenous respiration were observed immediately after irradiation. (auth)

Inhibition of Cell Division

The danger inherent in formulating specific models to explain physicsl- biological phenomena is discussed. Some of the phenomenological observations on effects of ionizing radiations on cell division in yeast are reviewed. Recent observations made on the modification of radiation damage in yeast by various envirommental agents are described. These findings are analyzed within the frameworks of the generalized migration model of Zirkle and Tobias and of the modified directaction model formulated by Alper, Howard-Flanders, Alexander, and others. 34 references. (C.H.)

The relation of metaphosphate formation to cell division in yeast

The relation of metaphosphate formation to cell division in yeast