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S Fogel

Publications and source records attributed to S Fogel.

At least 37 records · Page 2Linked to original sources
PubMed1990

Detection of induced mitotic chromosome loss in Saccharomyces cerevisiae--an interlaboratory assessment of 12 chemicals.

Induced mitotic chromosome loss was assayed using diploid yeast strain S. cerevisiae D61.M. The test relies upon the uncovering and expression of multiple recessive markers reflecting the presumptive loss of the chromosome VII homologue carrying the corresponding wild-type alleles. An interlaboratory study was performed in which 12 chemicals were tested under code in 2 laboratories. The results generated by the Berkeley and the Darmstadt laboratories were in close agreement. The solvents benzonitrile and methyl ethyl ketone induced significantly elevated chromosome loss levels. However, a treatment regime that included overnight storage at 0 degree C was required to optimize chromosome loss induction. Hence, these agents are postulated to induce chromosome loss via perturbation of microtubular assembly. Fumaronitrile yielded inconsistent results: induction of chromosome loss and respiratory deficiency was observed in both laboratories, but the response was much more pronounced in the Darmstadt trial than that observed in Berkeley. The mammalian carcinogens, benzene, acrylonitrile, trichloroethylene, 1,1,1-trichloroethane and 1,1,1,2-tetrachloroethane failed to induce chromosome loss but elicited high levels of respiratory deficiency, reflecting anti-mitochondrial activity. Trifluralin, cyclophosphamide monohydrate, diazepam and diethylstilbestrol dipropionate failed to induce any detectable genetic effects. These data suggest that the D61.M system is a reproducible method for detecting induced chromosome loss in yeast.

Alleles↗
PubMed1990

The detection of mitotic and meiotic chromosome gain in the yeast Saccharomyces cerevisiae: effects of methyl benzimidazol-2-yl carbamate, methyl methanesulfonate, ethyl methanesulfonate, dimethyl sulfoxide, propionitrile and cyclophosphamide monohydrate.

The diploid yeast strain BR1669 was used to study induction of mitotic and meiotic chromosome gain by selected chemical agents. The test relies on a gene dosage selection system in which hyperploidy is detected by the simultaneous increase in copy number of two alleles residing on the right arm of chromosome VIII: arg4-8 and cup1S (Rockmill and Fogel. 1988; Whittaker et al., 1988). Methyl methanesulfonate (MMS) induced mitotic, but not meiotic, chromosome gain. Methyl benzimidazol-2-yl carbamate (MBC) and ethyl methanesulfonate (EMS) induced both mitotic and meiotic chromosome gain. Propionitrile, a polar aprotic solvent, induced only mitotic chromosome gain; a reliable response was only achieved by overnight incubation of treated cultures at 0 degrees C. MBC is postulated to act by binding directly to tubulin. The requirement for low-temperature incubation suggests that propionitrile also induces aneuploidy by perturbation of microtubular dynamics. The alkylating agents MMS and EMS probably induce recombination which might in turn perturb chromosome segregation. Cyclophosphamide monohydrate and dimethyl sulfoxide (DMSO) failed to induce mitotic or meiotic chromosome gain.

Aneuploidy↗
PubMed1990

Mismatch repair-induced meiotic recombination requires the pms1 gene product.

The presence of multiple heterologies in a 9-kilobase (kb) interval results in a decrease in meiotic crossovers from 26.0% to 10.1%. There is also an increase from 3.5% to 11.1% in gene conversions and ectopic recombinations between the flanking homologous MAT loci. The hypothesis that mismatch repair of heteroduplex DNA containing several heterologies would lead to a second round of recombination has now been tested by examining the effect of a mutation that reduces mismatch correction. The repair-defective pms1-1 allele restores the pattern of recombination to nearly that seen in congenic diploids without the heterologies. Mismatch repair-induced recombination causes a significant increase in MAT conversions and ectopic recombination events with as few as two heterozygosities separated by 0.3-0.7 kb, but not when the mismatches are separated by greater than 1 kb. The frequency of these events depends on both the number and position of the heterozygosities relative to the flanking homologous MAT loci used to detect the events. The creation of recombinogenic lesions by mismatch repair in yeast could be analogous to the creation of recombinogenic lesions in dam- Escherichia coli. We suggest that the repair of heteroduplex DNA containing multiple mismatches may produce chromosomal rearrangements and gamete inviability when naturally polymorphic chromosomes undergo meiotic recombination.

Alleles↗
PubMed1989

The CUP2 gene product regulates the expression of the CUP1 gene, coding for yeast metallothionein.

The yeast CUP1 gene codes for a copper-binding protein similar to metallothionein. Copper sensitive cup1s strains contain a single copy of the CUP1 locus. Resistant strains (CUP1r) carry 12 or more multiple tandem copies. We isolated 12 ethyl methane sulfonate-induced copper sensitive mutants in a wild-type CUP1r parental strain, X2180-1A. Most mutants reduce the copper resistance phenotype only slightly. However, the mutant cup2 lowers resistance by nearly two orders of magnitude. We cloned CUP2 by molecular complementation. The smallest subcloned fragment conferring function was approximately 2.1 kb. We show that CUP2, which is on chromosome VII, codes for or controls the synthesis or activity of a protein which binds the upstream control region of the CUP1 gene on chromosome VIII. Mutant cup2 cells produced extremely low levels of CUP1-specific mRNA, with or without added copper ions and lacked a factor which binds to the CUP1 promoter. Integrated at the cup2 site, the CUP2 plasmid restored the basal level and inducibility of CUP1 expression and led to reappearance of the CUP1-promoter binding factor. Taken collectively, our data establish CUP2 as a regulatory gene for expression of the CUP1 metallothionein gene product.

Carrier Proteins↗
PubMed1989

Quantitative approaches for assessing chromosome loss in Saccharomyces cerevisiae: general methods for analyzing downturns in dose response.

Statistical methods are considered for analysis of data arising from a mitotic chromosome loss assay in Saccharomyces cerevisiae strain D61.M. The methods make use of reproducibility trial data from the assay (presented herein) and previous data, which suggest a unimodal, 'umbrella-patterned' dose response. Computer simulations are employed to illustrate the operating characteristics of the umbrella response methods. These methods are generally applicable to any toxicity assay that exhibits a downturn in dose response. Experimental design considerations are also discussed. These include applications of 2-stage sampling rules to first gauge the dose window of peak response, then test if the response deviates significantly from untreated levels.

Alleles↗
PubMed1989

Detection of induced mitotic chromosome loss in Saccharomyces cerevisiae--an interlaboratory study.

The diploid yeast strain D61.M was used to study induction of mitotic chromosome loss. The test relies upon the uncovering and expression of multiple recessive markers reflecting the presumptive loss of the chromosome VII homologue carrying the corresponding wild-type alleles. The underlying 'loss event' is probably complex since the predicted centromere-linked lethal tetrad segregations for chromosome VII are not recovered. Instead, the homologue bearing the multiple recessive markers is patently homozygous. An interlaboratory study was performed in which 16 chemicals were tested under code in 2 laboratories. The results generated by the Berkeley and Darmstadt laboratories were in close agreement. Acetonitrile, ethyl acetate, 4-acetylpyridine, propionitrile and nocodazole were identified as potent inducers of mitotic chromosome loss. Acetone, dimethyl sulfoxide and 2-methoxyethyl acetate either elicited weak responses or yielded ambiguous results. Water, carbon tetrachloride, 4-fluoro-D,L-phenylalanine, amphotericin B, griseofulvin, cadmium chloride, ethyl methanesulfonate and methylmercury(II) chloride failed to induce chromosome loss. These data suggest that the system described herein represents a reliable assay for chemically induced chromosome loss in yeast.

Alleles↗
PubMed1989

Cloning and nucleotide sequence of DNA mismatch repair gene PMS1 from Saccharomyces cerevisiae: homology of PMS1 to procaryotic MutL and HexB.

The PMS1 gene from Saccharomyces cerevisiae, implicated in DNA mismatch repair in yeast cells (M. S. Williamson, J. C. Game, and S. Fogel, Genetics 110:609-646, 1985), was cloned, and the nucleotide sequence was determined. The nucleotide sequence showed a 2,712-base-pair open reading frame; the predicted molecular mass of the deduced protein is 103 kilodaltons. Deletion mutants of the open reading frame were constructed and genetically characterized. The deduced amino acid sequence of the PMS1 gene exhibited homology to those of the mutL gene from Salmonella typhimurium and the hexB gene from Streptococcus pneumoniae, genes required for DNA mismatch repair in these organisms. The homology suggests an evolutionary relationship of DNA mismatch repair in procaryotes and eucaryotes.

Amino Acid Sequence↗
PubMed1989

Heteroduplex DNA correction in Saccharomyces cerevisiae is mismatch specific and requires functional PMS genes.

In vitro-constructed heteroduplex DNAs with defined mismatches were corrected in Saccharomyces cerevisiae cells with efficiencies that were dependent on the mismatch. Single-nucleotide loops were repaired very efficiently; the base/base mismatches G/T, A/C, G/G, A/G, G/A, A/A, T/T, T/C, and C/T were repaired with a high to intermediate efficiency. The mismatch C/C and a 38-nucleotide loop were corrected with low efficiency. This substrate specificity pattern resembles that found in Escherichia coli and Streptococcus pneumoniae, suggesting an evolutionary relationship of DNA mismatch repair in pro- and eucaryotes. Repair of the listed mismatches was severely impaired in the putative S. cerevisiae DNA mismatch repair mutants pms1 and pms2. Low-efficiency repair also characterized pms3 strains, except that correction of single-nucleotide loops occurred with an efficiency close to that of PMS wild-type strains. A close correlation was found between the repair efficiencies determined in this study and the observed postmeiotic segregation frequencies of alleles with known DNA sequence. This suggests an involvement of DNA mismatch repair in recombination and gene conversion in S. cerevisiae.

Alleles↗
PubMed1989

The CUP2 gene product, regulator of yeast metallothionein expression, is a copper-activated DNA-binding protein.

CUP2 is a regulatory gene controlling expression of CUP1, which encodes the Cu-binding yeast metallothionein. CUP2, which is identical to the ACE1 gene, encodes a Cu-regulated DNA-binding protein. The CUP2 protein contains a cysteine-rich DNA-binding domain dependent on Cu+ and Ag+ ions which bind the cysteine residues and direct the refolding of the metal-free apoprotein. CUP2 mutant alleles from Cu-sensitive yeast strains have point mutations affecting the DNA-binding activity. These results establish CUP2 as the primary sensor of intracellular Cu+ in the yeast Saccharomyces cerevisiae, functioning as a Cu+-regulated transcriptional activator.

Amino Acid Sequence↗
PubMed1988

The molecular genetics of copper resistance in Saccharomyces cerevisiae--a paradigm for non-conventional yeasts.

After a short introduction on the historical background of the development of Saccharomyces cerevisiae as a model eukaryote, a review is given on the present state of genetics and molecular biology of copper resistance in S. cerevisiae. The gene CUP1 encodes a protein (copper metallothionein) of a molecular weight of 6570 dalton. The synthesis of this copper chelatin is induced by copper and is regulated at the level of transcription. Copper resistance (CUPr) is correlated with amplification of CUP1 and resulted in a higher copy number of this gene on chromosome VIII. Spontaneous meiotic alterations of the gene copy number have been studied.

Carrier Proteins↗
PubMed1988

The detection of mitotic and meiotic aneuploidy in yeast using a gene dosage selection system.

A system is described in which spontaneous and chemically-induced mitotic and meiotic hyperploidy can be assayed in the same diploid culture of Saccharomyces cerevisiae. Monitoring gene dosage changes at two loci on chromosome VIII, the test utilizes a leaky temperature-sensitive allele arg4-8 and low level copper resistance conferred by the single copy allele cup1s. An extra chromosome VIII provides simultaneous increased dosage for both genes, resulting in colonies that are both prototrophic for arginine at 30 degrees C and copper resistant. During mitotic cell divisions in diploids, spontaneous chromosome VIII hyperploids (trisomes and tetrasomes) occur at a frequency of 6.4 x 10(-6) per viable cell. Among ascospores, the spontaneous chromosome VIII disome frequency is 5.5 x 10(-6) per viable spore. The tubulin-binding reagent methyl benzimidazol-2-yl carbamate (MBC) elicits enhanced levels of mitotic and meiotic aneuploidy relative to control levels. The system represents a novel model for examining chromosome behavior during mitosis and meiosis and provides a sensitive and quantifiable procedure for examining chemically induced aneuploidy.

Aneuploidy↗
PubMed1988

DIS1: a yeast gene required for proper meiotic chromosome disjunction.

Mutants at a newly identified locus, DIS1 (disjunction), were detected by screening for mutants that generate aneuploid spores (chromosome VIII disomes) at an increased frequency. Strains carrying the partially dominant alleles, DIS1-1 or DIS1-2, generate disomes at rates up to 100 times the background level. Mitotic nondisjunction is also increased 10- to 50-fold over background. Half-tetrad analysis of disomes for a marked interval on chromosome VIII yields wild-type map distances, indicating that a general recombination deficiency is not the cause of nondisjunction. Meiotic nondisjunction in DIS1 mutants is not chromosome specific; 5% of the spores disomic for chromosome VIII are also disomic for chromosome III. Although only one disomic spore is found per exceptional ascus most of the disomes appear to be generated in the first meiotic division because recovered chromosome VIII disomes contain mostly nonsister chromosomes. We propose that disome generation in the DIS1 mutants results from precocious separation of sister centromeres.

Aneuploidy↗
PubMed1988

A DNA sequence conferring high postmeiotic segregation frequency to heterozygous deletions in Saccharomyces cerevisiae is related to sequences associated with eucaryotic recombination hotspots.

The meiotic behavior of two graded series of deletion mutations in the ADE8 gene in Saccharomyces cerevisiae was analyzed to investigate the molecular basis of meiotic recombination. Postmeiotic segregation (PMS) was observed for a subset of the deletion heterozygosities, including deletions of 38 to 93 base pairs. There was no clear relationship between deletion length and PMS frequency. A common sequence characterized the novel joint region in the alleles which displayed PMS. This sequence is related to repeated sequences recently identified in association with recombination hotspots in the human and mouse genomes. We propose that these particular deletion heterozygosities escape heteroduplex DNA repair because of fortuitous homology to a binding site for a protein.

Alleles↗
PubMed1987

Synaptic relations in meiotic gene conversion at the iterated CUP1r locus of S. cerevisiae.

This study concerns a comparative molecular analysis of copy number changes in two hybrids that differ in the extent of homologies at the CUP1r locus. Hybrid JW1020 is a diploid wherein each parent contributed nine identical, tandemly arrayed 2.0 kb repeat units. Genomic DNA was isolated from each of the spore colonies in a sample of 200 unselected tetrads. About 15% displayed copy number changes, i.e., increases or decreases of one or more complete units. Changes on a per tetrad basis occurred as often in a single spore colony as changes in each of two spores. Such double changes are rarely reciprocal in character. To account for the observed qualitative and quantitative copy number shifts, we propose a molecular recombination model that posits partial, incomplete synaptic pairing and gene conversion of the unpaired regions with or without associated crossing over. A second contrasting study centers on the copy number alterations and recombinational events uncovered in a molecular analysis of 50 unselected tetrads generated by hybrid EB8. Unlike the hybrid JW1020, the EB8 diploid strain carried a six copy tandem array of 1.1 kb units at the CUP1r locus in one parental homologue and a five copy array of 1.6 kb units at the corresponding chromosome VIII locus. These natural alleles were recovered from industrial yeast strains by conventional genetic procedures and characterized by restrictional analysis. Twelve tetrads exhibit evidence for several different types of recombination events. However,ordinary crossover exchanges are conspicuously absent. We suppose that the repetitious nonhomologies generate DNA configurations sufficient to disrupt the effective synapsis over the entire locus.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrier Proteins↗
PubMed1987

Gene conversion, unequal crossing-over and mispairing at a non-tandem duplication during meiosis of Saccharomyces cerevisiae.

We have developed a novel system to examine conversion, exchange and mispairing involving a non-tandem duplication of the ade8 locus in yeast by monitoring the segregation of heterozygous markers between the duplicated sequence. Plasmid Yrp17 carries the yeast selectable markers URA3+ and TRP1+. Yrp17 derivatives with a 4 kb insert carrying ade8-18 were used to clone the mutations trp1-1 and ura3-1 by gap repair. Integrants of the resulting plasmids at the Ade8 locus were crossed to yield diploid hybrids with a non-tandem duplication of Ade8 and heterozygosity for the plasmid markers between the duplicated sequences. 1192 complete, unselected asci were analyzed and 270 exhibiting recombination of the markers contributed by the plasmid were analyzed by Southern transfers to detect changes in plasmid sequences. Twenty-seven tetrads had unequal homologous exchanges and five had unequal sister-chromatid exchanges. Seven tetrads carry an additional copy of the integrated plasmid and ten are missing one. We propose that these two classes represent conversions of the entire 11 kb plasmid, which occur after misalignment and formation of an unpaired loop. Mispairing is a frequent event, and occurs in approximately fifty percent of all meioses. The system described provides a means to determine the meiotic rules of conversion, exchange and pairing for duplicated DNA sequences.

Crosses, Genetic↗
PubMed1986

Biodegradation of chlorinated ethenes by a methane-utilizing mixed culture.

Chlorinated ethenes are toxic substances which are widely distributed groundwater contaminants and are persistent in the subsurface environment. Reports on the biodegradation of these compounds under anaerobic conditions which might occur naturally in groundwater show that these substances degrade very slowly, if at all. Previous attempts to degrade chlorinated ethenes aerobically have produced conflicting results. A mixed culture containing methane-utilizing bacteria was obtained by methane enrichment of a sediment sample. Biodegradation experiments carried out in sealed culture bottles with radioactively labeled trichloroethylene (TCE) showed that approximately half of the radioactive carbon had been converted to 14CO2 and bacterial biomass. In addition to TCE, vinyl chloride and vinylidene chloride could be degraded to products which are not volatile chlorinated substances and are therefore likely to be further degraded to CO2. Two other chlorinated ethenes, cis and trans-1,2-dichloroethylene, were shown to degrade to chlorinated products, which appeared to degrade further. A sixth chlorinated ethene, tetrachloroethylene, was not degraded by the methane-utilizing culture under these conditions. The biodegradation of TCE was inhibited by acetylene, a specific inhibitor of methane oxidation by methanotrophs. This observation supported the hypothesis that a methanotroph is responsible for the observed biodegradations.

1-Propanol↗
PubMed1985

Meiotic recombination and sporulation in repair-deficient strains of yeast.

A genetic system designed to monitor recombination and sporulation in various repair-deficient yeast strains was constructed. Variously heterozygous at seven or eight sites distributed across the genome, the system facilitated sensitive detection of changes in frequency or pattern of meiotic recombination. Ten rad mutants sensitive primarily to UV-irradiation and without terminal blocks in the sporulation process were studied. Seven were defective in excision repair (rad1, rad2, rad3, rad4, rad10, rad14 and rad16), and three were defective in mutagenic repair (rad5, rad9 and rad18). Individually, each mutant displayed behavior consistent with an orthodox meiosis including a wild-type meiotic recombination profile with respect to gene conversion, PMS and intergenic map distances. Accordingly, we conclude that these mutants are without major effect on meiotic heteroduplex formation or correction. However, certain combinations of excision-defective mutants with rad18 exhibited marked ascosporal inviability. Tetraploids homozygous for rad1 and rad18 produce a large proportion of diploid spores containing a recessive lethal.

DNA Repair↗