scholarly journals INCREASED SPONTANEOUS MITOTIC SEGREGATION IN MMS-SENSITIVE MUTANTS OF SACCHAROMYCES CEREVISIAE

Genetics ◽  
1977 ◽  
Vol 87 (2) ◽  
pp. 229-236
Author(s):  
Satya Prakash ◽  
Louise Prakash
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Methyl Methanesulfonate ◽  
X Rays ◽  
X Ray ◽  
Complementation Groups

ABSTRACT Methyl methanesulfonate (MMS)-sensitive mutants of Saccharomyces cerevisiae belonging to four different complementation groups, when homozygous, increase the rate of spontaneous mitotic segregation to canavanine resistance from heterozygous sensitive (canr/+) diploids by 13- to 170-fold. The mms8—1 mutant is MMS and X-ray sensitive and increases the rate of spontaneous mitotic segregation 170-fold. The mms9—1 and mms13—1 mutants are sensitive to X rays and UV, respectively, in addition to MMS, and increase the rate of spontaneous mitotic segregation by 13-fold and 85-fold, respectively. The mutant mms21—1 is sensitive to MMS, X rays and UV and increases the rate of spontaneous mitotic segregation 23-fold.

scholarly journals ISOLATION AND CHARACTERIZATION OF MMS-SENSITIVE MUTANTS OF SACCHAROMYCES CEREVISIAE

Genetics ◽  
1977 ◽  
Vol 86 (1) ◽  
pp. 33-55 ◽  
Author(s):  
Louise Prakash ◽  
Satya Prakash
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Repair ◽  
Methyl Methanesulfonate ◽  
X Rays ◽  
Isolation And Characterization ◽  
Complementation Groups ◽  
The Cross

ABSTRACT We have isolated mutants sensitive to methyl methanesulfonate (MMS) in Saccharomyces cerevisiae. Alleles of rad1, rad4, rad6, rad52, rad55 and rad57 were found among these mms mutants. Twenty-nine of the mms mutants which complement the existing radiation-sensitive (rad and rev) mutants belong to 22 new complementation groups. Mutants from five complementation groups are sensitive only to MMS. Mutants of 11 complementation groups are sensitive to UV or X rays in addition to MMS, mutants of six complementation groups are sensitive to all three agents. The cross-sensitivities of these mms mutants to UV and X rays are discussed in terms of their possible involvement in DNA repair. Sporulation is reduced or absent in homozygous diploids of mms mutants from nine complementation groups.

scholarly journals MATING-TYPE REGULATION OF METHYL METHANESULFONATE SENSITIVITY IN SACCHAROMYCES CEREVISIAE

Genetics ◽  
1980 ◽  
Vol 95 (2) ◽  
pp. 259-271
Author(s):  
George P Livi ◽  
Vivian L Mackay
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mating Type ◽  
S Phase ◽  
Methyl Methanesulfonate ◽  
Survival Curves ◽  
Repair Capacity ◽  
Type Locus ◽  
X Ray ◽  
G2 Phase ◽  
Diploid Cells

ABSTRACT Heterozygosity at the mating-type locus (MAT) in Saccharomyces cerevisiae has been shown previously to enhance X-ray survival in diploid cells. We now show that a/α diploids are also more resistant to the radiomimetic agent methyl methanesulfonate (MMS) that are diploids that are homozygous at MAT (i.e., either a/a or α/α). Log-phase a/α cultures exhibit biphasic MMS survival curves, in which the more resistant fraction consists of budded cells (those cells in the S and G2 phases of the cell cycle). Survival curves for log-phase cultures of a/a or α/α diploids have little if any biphasic nature, suggesting that the enhanced S- and G2-phase repair capacity of a/α cells may be associated with heterozygosity at MAT. The survival of cells arrested at the beginning of the S phase with hydroxyurea indicates that MAT-dependent MMS repair is limited to S and G2, whereas MAT-independent repair can occur in Gl.

scholarly journals X-ray Tomography Generates 3-D Reconstructions of the Yeast, Saccharomyces cerevisiae, at 60-nm Resolution

2004 ◽  
Vol 15 (3) ◽  
pp. 957-962 ◽  
Author(s):  
Carolyn A. Larabell ◽  
Mark A. Le Gros
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Imaging Technique ◽  
Three Dimensional ◽  
X Rays ◽  
Yeast Saccharomyces Cerevisiae ◽  
High Resolution Data ◽  
X Ray ◽  
Whole Cells ◽  
Order Of Magnitude ◽  
Time Required

We examined the yeast, Saccharomyces cerevisiae, using X-ray tomography and demonstrate unique views of the internal structural organization of these cells at 60-nm resolution. Cryo X-ray tomography is a new imaging technique that generates three-dimensional (3-D) information of whole cells. In the energy range of X-rays used to examine cells, organic material absorbs approximately an order of magnitude more strongly than water. This produces a quantifiable natural contrast in fully hydrated cells and eliminates the need for chemical fixatives or contrast enhancement reagents to visualize cellular structures. Because proteins can be localized in the X-ray microscope using immunogold labeling protocols (Meyer-Ilse et al., 2001. J. Microsc. 201, 395–403), tomography enables 3-D molecular localization. The time required to collect the data for each cell shown here was <15 min and has recently been reduced to 3 min, making it possible to examine numerous yeast and to collect statistically significant high-resolution data. In this video essay, we show examples of 3-D tomographic reconstructions of whole yeast and demonstrate the power of this technology to obtain quantifiable information from whole, hydrated cells.

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

1987 ◽  
Vol 7 (3) ◽  
pp. 1078-1084 ◽  
Author(s):  
G M Cole ◽  
D Schild ◽  
S T Lovett ◽  
R K Mortimer
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Damage ◽  
Gene Fusion ◽  
Dna Recombination ◽  
Methyl Methanesulfonate ◽  
Lacz Gene ◽  
Gene Fusions ◽  
X Rays ◽  
Diploid Cells ◽  
Beta Galactosidase

The RAD52 and RAD54 genes in the yeast Saccharomyces cerevisiae are involved in both DNA repair and DNA recombination. RAD54 has recently been shown to be inducible by X-rays, while RAD52 is not. To further investigate the regulation of these genes, we constructed gene fusions using 5' regions upstream of the RAD52 and RAD54 genes and a 3'-terminal fragment of the Escherichia coli beta-galactosidase gene. Yeast transformants with either an integrated or an autonomously replicating plasmid containing these fusions expressed beta-galactosidase activity constitutively. In addition, the RAD54 gene fusion was inducible in both haploid and diploid cells in response to the DNA-damaging agents X-rays, UV light, and methyl methanesulfonate, but not in response to heat shock. The RAD52-lacZ gene fusion showed little or no induction in response to X-ray or UV radiation nor methyl methanesulfonate. Typical induction levels for RAD54 in cells exposed to such agents were from 3- to 12-fold, in good agreement with previous mRNA analyses. When MATa cells were arrested in G1 with alpha-factor, RAD54 was still inducible after DNA damage, indicating that the observed induction is independent of the cell cycle. Using a yeast vector containing the EcoRI structural gene fused to the GAL1 promoter, we showed that double-strand breaks alone are sufficient in vivo for induction of RAD54.

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

1987 ◽  
Vol 7 (3) ◽  
pp. 1078-1084
Author(s):  
G M Cole ◽  
D Schild ◽  
S T Lovett ◽  
R K Mortimer
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Damage ◽  
Gene Fusion ◽  
Dna Recombination ◽  
Methyl Methanesulfonate ◽  
Lacz Gene ◽  
Gene Fusions ◽  
X Rays ◽  
Diploid Cells ◽  
Beta Galactosidase

The RAD52 and RAD54 genes in the yeast Saccharomyces cerevisiae are involved in both DNA repair and DNA recombination. RAD54 has recently been shown to be inducible by X-rays, while RAD52 is not. To further investigate the regulation of these genes, we constructed gene fusions using 5' regions upstream of the RAD52 and RAD54 genes and a 3'-terminal fragment of the Escherichia coli beta-galactosidase gene. Yeast transformants with either an integrated or an autonomously replicating plasmid containing these fusions expressed beta-galactosidase activity constitutively. In addition, the RAD54 gene fusion was inducible in both haploid and diploid cells in response to the DNA-damaging agents X-rays, UV light, and methyl methanesulfonate, but not in response to heat shock. The RAD52-lacZ gene fusion showed little or no induction in response to X-ray or UV radiation nor methyl methanesulfonate. Typical induction levels for RAD54 in cells exposed to such agents were from 3- to 12-fold, in good agreement with previous mRNA analyses. When MATa cells were arrested in G1 with alpha-factor, RAD54 was still inducible after DNA damage, indicating that the observed induction is independent of the cell cycle. Using a yeast vector containing the EcoRI structural gene fused to the GAL1 promoter, we showed that double-strand breaks alone are sufficient in vivo for induction of RAD54.

scholarly journals THE INDUCTION OF MITOTIC GENE CONVERSION BY X-IRRADIATION OF HAPLOID SACCHAROMYCES CEREVISIAE

Genetics ◽  
1973 ◽  
Vol 74 (2) ◽  
pp. 243-258
Author(s):  
D A Campbell
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Gene Conversion ◽  
Colony Formation ◽  
X Rays ◽  
Zygote Formation ◽  
X Ray ◽  
Sister Chromatids ◽  
X Irradiation ◽  
Radiation Induced ◽  
Mitotic Gene Conversion

ABSTRACT Mitotic recombination in Saccharomyces cerevisiae was examined by means of experiments in which one of the haploid parents was X-irradiated prior to zygote formation. By this method radiation-induced lesions are restricted to only one of the two non-sister chromatids that may be expected to undergo mitotic exchange in the diploid. The principal results of this work are: (1) X-irradiated haploid cells that are incapable of further vegetative growth (colony formation) are efficiently rescued into viable diploids by mating with unirradiated haploid cells. (2) X-rays delivered to only one of the two haploid parents are recombinogenic in the resultant diploid. The frequency of detected recombinational events increases as a probable linear function of the X-ray dose. (3) A majority of the induced recombinational events are nonreciprocal in nature (mitotic gene conversion). These results complement those obtained from X-irradiation of the vegetative diploid itself, where the induced genetic exchanges are principally reciprocal.

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

Chemical Species Identification in an SEM by Changes in Emitted X-Ray Energies

1974 ◽  
Vol 32 ◽  
pp. 570-571
Author(s):  
R. H. Duff
Keyword(s):  
Species Identification ◽  
Valence Electron ◽  
Chemical Species ◽  
X Rays ◽  
Chemical Bonds ◽  
Small Shift ◽  
X Ray ◽  
Electron Transitions ◽  
Peak Energy ◽  
Chemical Combination

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.

Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

1977 ◽  
Vol 35 ◽  
pp. 328-329
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Thin Foil ◽  
Electron Excitation ◽  
Simple Approach ◽  
Foil Thickness ◽  
X Rays ◽  
X Ray ◽  
Hole Spectrum ◽  
Illumination System ◽  
Thin Foils ◽  
Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

X-ray micro tomography in the scanning electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 106-107 ◽  
Author(s):  
W. Brünger
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Target Surface ◽  
The Body ◽  
X Rays ◽  
Cross Sectional ◽  
X Ray ◽  
Micro Tomography ◽  
Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

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