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S Fogel

Publications and source records attributed to S Fogel.

At least 73 records · Page 4Linked to original sources
PubMed1976

Nuclear and mitochondrial DNA replication during zygote formation and maturation in yeast.

Nuclear and mitochondrial DNA replication were monitered during the development of synchronous yeast zygotes. Purified first zygotic buds were also analyzed. Nuclear DNA replicated discontinuously but coincidently with bud initiation, while mitochondrial DNA replicated throughout the zygotic formation and maturation period. First zygotic buds contained the diploid level of both nuclear and mitochondrial DNA.

Cell Nucleus↗
PubMed1975

Mitotic chromosome loss in a disomic haploid of Saccharomyces cerevisiae.

Experiments designed to characterize the incidence of mitotic chromosome loss in a yeast disomic haploid were performed; The selective methods employed utulize the non-mating property of strains disomic for linkage group III and heterozygous at the mating type locus. The principal findings are: (1) The grequency of spontaneous chromosome loss in the disome is of the order 10- minus 4 per cell; this value approximates the frequency in the same population of spontaneous mitotic exchange resulting in homozygosity at the mating type locus. (2) The recovered diploids are pure clones, and thus represent unique events in the disomic haploid. (3) Of the euploid chromosomes recovered after events leading to chromosome loss, approximately 90% retain the parental marker configuration expected from segregation alone; however, the remainder are recombinant for marker genes, and are the result of mitotic exchanges in the disome, especially in regions near the centromere. The recombinant proportion significantly exceeds that expected if chromosome loss and mitotic exchange in the disome were independent events. The data are consistent with a model proposing mitotic nondisjunction as the event responsible for chromosome loss in the disomic haploid.

Chromosome Mapping↗
PubMed1975

Nuclear and mitochondrial deoxyribonucleic acid replication during mitosis in Saccharomyces cerevisiae.

To study nuclear and mitochondrial deoxyribonucleic acid (DNA) synthesis during the cell cycle, a 15N-labeled log-phase population of Saccharomyces cervisiae was shifted to 14N medium. After one-half generation, the cells were centrifuged on a sorbitol gradient in a zonal rotor to fractionate the population according to cell size and age into fractions representing the yeast cell cycle. DNA samples isolated from the zonal rotor cell samples were centrifuged to equilibrium in CsC1 in an analytical ultracentrifuge to separate the nuclear and mitochondrial DNA components. The amount of 14N incorporated into each 15N-labeled DNA species was measured. The extent of nuclear DNA replication per sample was obtained by measuring the amount of hybrid DNA. The percentage of hybrid nuclear DNA increased from 6 to 68% and then decreased to 44% during the cell cycle. Upon ultracentrifugation, mitochondrial DNA banded as a unimodal peak in all zonal rotor samples. Mitochondrial DNA replication could be ascertained only by the 14N level in each mitochondrial peak and not, as with nuclear DNA, by hybrid DNA level. In contrast to the nuclear incorporation pattern, the 14N percentage in mitochondrial DNA remained effectively constant during the cell cycle. Comparison of the data to theoretical distributions showed that nuclear DNA was replicated discontinuously during the cell cycle, whereas mitochondrial DNA was replicated continuously throughout the entire mitotic cycle.

Cell Nucleus↗
PubMed1973

Synchronous mating in yeast.

Homogeneous a and alpha unbudded yeast cells in logarithmic phase, grown in supplemented minimal medium and isolated by zonal gradient centrifugation, are used for mating. When these cells are resuspended in aerated defined medium, highly synchronous mating rapidly occurs. Within 20 min of incubation at 30 degrees early sexual pairing is evident; extensive agglutination is observed by 60 min, and cell fusion and bud initiation in zygotes occurs after 60-140 min. Sorbitol gradient fractionation of mating mixtures taken at various times during incubation allows the isolation of zygotes or unmated cells. Zygote preparations 90-95% purified are obtained in quantities suitable for genetic and biochemical analysis. The mating procedure is predictable and reproducible.

Agglutination↗
PubMed1972

Conversion-associated recombination in yeast (hybrids-meiosis-tetrads-marker loci-models).

Gene conversion and conversion-associated reciprocal recombination have been studied in various Saccharomyces cerevisiae hybrids. In a sample of 11,023 unselected meiotic tetrads, 907 conversions were observed at the arg4, thr3, his1, and SUP6 loci. Of these conversions, 445 (or 49.1%) were associated with reciprocal recombination of bracketing markers no more than 20-centimorgans apart. For conversions of two other loci, his2 and thr1, for which the bracketing markers were more than 20-centimorgans apart, recombination frequencies were significantly greater than 50%. These findings are discussed in terms of current models of genetic recombination. It is suggested that all meiotic crossing-over is characterized by the recombination events that are associated with conversion.

Alleles↗
PubMed1971

Chemical detection of microbial prey by bacterial predators.

A motile, predacious bacterium which degraded Pythium debaryanum was strongly attracted to substances released into the medium by the fungus. A nonpredacious bacterium was not attracted to these substances. The predator bacterium was specifically attracted to cellulose and its oligomers which are known to be components of the cell wall of Pythium. Ethanol inhibited chemotaxis of the bacterium without affecting either its motility or its ability to degrade cellulose. A second predacious bacterium was isolated for the alga, Skeletonema costatum. The role of chemoreception in the detection of microbial prey by bacterial predators in natural habitats is discussed.

Agar↗
PubMed1969

Informational transfer in meiotic gene conversion.

Aberrant meiotic segregations attributable to intragenic events have been analyzed in an unselected sample of 1611 tetrads from three heteroallelic diploids of Saccharomyces cerevisiae. Reciprocal recombination between alleles accounts for only a minor fraction of the total aberrant tetrads, while the majority component is represented by single- and double-site conversions. The frequency of double-site conversion is inversely related to the physical length of the interallelic interval. Since double-site conversions do not yield prototrophs, their occurrence leads to biased estimates of intragenic distances. Conversion is viewed as a process of informational transfer distinct from conventional crossing-over. The implications of the findings for genetic fine structure mapping and evolutionary theory are discussed briefly.

Alleles↗