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  • 1
    ISSN: 1432-0983
    Keywords: Key words Yeast ; RPD3 (REC3) ; Mitotic recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Prior research identified the recessive rec3-1ts mutation in Saccharomyces cerevisiae which, in homozygous diploid cells, confers a conditional phenotype resulting in reduced levels of spontaneous mitotic recombination and loss of sporulation at the restrictive temperature of 36 °C. We found that a 3.4-kb genomic fragment that complements the rec3-1ts/rec3-1ts mutation and which maps to chromosome XIV, is identical to RPD3, a gene encoding a histone de-acetylase. Sporulation is reduced in homozygous diploid strains containing the rec3-1ts allele at 24 °C, suggesting that this allele of RPD3 encodes a gene product with a reduced function. Sporulation is abolished in diploid strains homozygous for the rpd3Δ or rec3-1ts alleles, as well as in rpd3Δ/rec3-1ts heteroallelic diploids, at the non-permissive temperature. Acid-phosphatase expression has been shown to be RPD3 dependent. We found that acid-phosphatase activity is greater in diploid strains homozygous for the temperature-sensitive rec3-1ts allele than in RPD3/RPD3 strains and increased further when mutant strains are grown at 36 °C. We also tested the rpd3Δ/rpd3Δ strains for their effects on spontaneous mitotic recombination. By assaying a variety of intra- and inter-genic recombination events distributed over three chromosomes, we found that in the majority of cases spontaneous mitotic recombination was reduced in diploid rpd3Δ/rpd3Δ cells (relative to a RPD3/RPD3 control). Finally, although 90% of mitotic recombinant events are initiated in the G1 phase of the growth cycle (i.e., before DNA synthesis) we show that RPD3 is not regulated in a cell-cycle-dependent manner. These data suggest that mitotic recombination, in addition to gene expression, is affected by changes in chromatin architecture mediated by RPD3.
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  • 2
    ISSN: 1432-0983
    Keywords: Chromosomal stability ; Recombination ; Mitosis ; Meiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The recessive hyperrecombination mutation rec46-1, isolated by ultraviolet light mutagenesis of the MATα n+1 chromosome VII disomic strain LBW (Esposito et al. 1982), enhances the mitotic rates of spontaneous gene conversion, intergenic recombination and restitution of haploidy (due to chromosomal loss or mitotic nondisjunction) in MATα n+1 chromosome VII disomic strains. The rec46-1 mutation does not prevent HO directed homothallic interconversion of mating types. MATaIMaTα ree46-1/rec46-1 diploids exhibit the same degree of hyperrecombinational activity as MATα rec46-1 n+1 chromosome VII disomics with respect to gene conversion and intergenic recombination resulting in prototrophy. When compared to MATα rec46-1 n+1 disomics however, MATa/MATα rec46-1/rec46-1 diploids exhibit a ten fold reduced level of hyperrecombinational activity with respect to intergenic recombination and present no evidence of chromosomal loss or nondisjunction resulting in 2n-1 monosomic segregants. MATaIMATα rec46-1/rec46-1 diploids are sporulation-deficient. The results obtained demonstrate that the REC46 gene product modulates mitotic chromosomal stability and recombination and is essential for sporulation (meiosis and ascospore formation).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 25 (1994), S. 1-11 
    ISSN: 1432-0983
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0983
    Keywords: Sporulation (S. cerevisiae) ; Protein and RNA synthesis ; Antibiotic sensitivities ; Mating type ; Mitochondrial controls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The purpose of the experiments reported below was to examine the response in sporulation medium of the three diploid cell types MATα MATα, MATα MATα (asporogenic diploids) and MATα MATα (sporogenic diploid) to erythromycin, a specific inhibitor of mitochondrial protein synthesis (MPS) in vegetative cultures, and cycloheximide, a specific inhibitor of cytosol protein synthesis (CPS) in vegetative cultures. When MATα MATα diploids are transferred to sporulation medium a significant fraction of total protein synthesis (CPS + MPS) becomes sensitive to erythromycin in contrast to the behavior of MATa MATa and MATα MATα diploids in which the resistance of CPS to erythromycin is maintained. The decompartmentalization of erythromycin sensitivity is thus cell type specific. Erythromycin stimulates total RNA synthesis of MATα MATα cells in sporulation medium but not of MATα MATα and MATα MATα cells. Cycloheximide inhibits protein synthesis and stimulates RNA synthesis in all three diploid cell types. An erythromycin resistant mutant, shown to be due to a mutation of the mitochondrial genome, exhibited only partial resistance of CPS to erythromycin in sporulation medium in the background of the MATα MATα mating type genotype. Total RNA synthesis in this mutant was not stimulated. The results reported indicate that mitochondrial functions during sporulation are not restricted to those involving respiratory metabolism.
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  • 5
    ISSN: 1432-0983
    Keywords: Chromosomal loss ; Mitotic nondisjunction ; Gene conversion ; Mitotic recombination ; Ultraviolet light
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have employed a hyperhaploid strain of Saccharomyces cerevisiae disomic for chromosome VII to monitor spontaneous and ultraviolet light induced restitution of haploidy (chromosomal loss and/or nondisjunction), mitotic gene conversion and mitotic intergenic recombination. The disomic chromosomal pair incorporates six heterozygous markers, including cyh2 r, distributed on both sides of the centromere. Cycloheximide resistant segregants of spontaneous origin were analyzed to calculate the spontaneous mitotic rates of restitution of haploidy, intergenic recombination and gene conversion that result in expression of the cyh2 r mutation. Restitution of haploidy was found to be the most common source of spontaneously arising cycloheximide resistant segregants. In contrast, those induced by ultraviolet light resulted most frequently from gene conversion of CYH2 s to cyh2 r. The chromosome VII hyperhaploid system provides a sensitive method to detect the aneugenic and recombinagenic effects of suspect chemical and physical agents.
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  • 6
    ISSN: 1432-0983
    Keywords: S. cerevisiae ; Spontaneous mutation ; Mitotic segregation ; Loss of heterozygosity ; Recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have employed the analysis of spontaneous forward mutations that confer the ability to utilize L-α-aminoadipate as a nitrogen source (α-Aa+) to discern the events that contribute to mitotic segregation of spontaneous recessive mutations by diploid cells. α-Aa- diploid cells yield α-Aa+ mutants at a rate of 7.8±3.6×10-9. As in haploid strains, approximately 97% (30/31) of α-Aa+ mutants are spontaneous lys2-x recessive mutations. α-Aa+ mutants of diploid cells reflect mostly the fate of LYS2/lys2-x heterozygotes that arise by mutation within LYS2/LYS2 populations at a rate of 1.2±0.4×10-6. Mitotic recombination occurs in nonrandom association with forward mutation of LYS2 at a rate of 1.3±0.6×10-3. This mitotic recombination rate is tenfold higher than that of a control LYS2/lys2-1 diploid. Mitotic segregation within LYS2/lys2-x subpopulations yields primarily lys2-x/lys2-x diploids and a minority of lys2-x aneuploids. Fifteen percent of lys2-x/lys2-x diploids appear to have arisen by gene conversion of LYS2 to lys2-x; 85% of lys2-x/lys2-x diploids appear to have arisen by mitotic recombination in the CENII-LYS2 interval. lys2-1/lys2-1 mitotic segregants of a control LYS2/lys2-1 diploid consist similarly of 18% of lys2-1/lys2-1 diploids that appear to have arisen by gene conversion of LYS2 to lys2-1 and 82% of lys2-1/lys2-1 diploids that appear to have arisen by mitotic recombination in the CENII-LYS2 interval. The methods described can be used to simultaneously monitor the effects of yeast gene mutations and carcinogens on the principal parameters affecting the genomic stability of diploid mitotic cells: mutation, gene conversion, intergenic recombination, and chromosomal loss or rearrangement.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 23 (1993), S. 430-434 
    ISSN: 1432-0983
    Keywords: S. cerevisiae ; Mutational homozygosis ; Loss of heterozygosity ; Mutation ; Recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A leucine-requiring hybrid of Saccharomyces cerevisiae, homoallelic at the LEU1 locus (leu1–12/leu1–12) and heterozygous for three chromosome-VII genetic markers distal to the LEU1 locus, was employed to inquire: (1) whether spontaneous gene mutation and mitotic segregation of heterozygous markers occur in positive nonrandom association and (2) whether homozygous LEU1/LEU1 mutant diploids are generated. The results demonstrate that gene mutation of leu1–12 to LEU1 and mitotic segregation of heterozygous chromosome-VII markers occur in strong positive nonrandom association, suggesting that the stimulatory DNA lesion is both mutagenic and recombinogenic. In addition, genetic analysis of diploid Leu+ revertants revealed that approximately 3% of mutations of leu1–12 to LEU1 result in LEU1/LEU1 homozygotes. Red-white sectored Leu+ colonies exhibit genotypes that implicate postreplicational chromatid breakage and exchange near the site of leu1–12 reversion, chromosome loss, and subsequent restitution of diploidy, in the sequence of events leading to mutational homozygosis. By analogy, diploid cell populations can yield variants homozygous for novel recessive gene mutations at biologically significant rates. Mutational homozygosis may be relevant to both carcinogenesis and the evolution of asexual diploid organisms.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 1 (1980), S. 241-248 
    ISSN: 1432-0983
    Keywords: Recombination Hyper-rec mutants Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary As part of a comparative analysis of spontaneous mitotic and meiotic recombination we have compared the mitotic and meiotic maps of the wild type and yeast hybrids homozygous for reml-l, a mitosis-specific hyper-rec mutation (Golin and Esposito, 1977; Golin, 1979). In wild type yeast strains recombination in centromere proximal intervals occurs relatively more frequently in mitosis than in meiosis. In reml-1/rem1-1 hybrids the distribution of mitotic exchange events is more similar to the distribution observed in meiosis.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 17 (1990), S. 7-12 
    ISSN: 1432-0983
    Keywords: REC genes ; Recombination ; Gene conversion ; Sporulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have isolated and characterized three conditional hyporecombination mutants, rec1-1, rec3-1 and rec4-1, that define three REC genes of Saccharomyces cerevisiae required for spontaneous general mitotic interchromosomal recombination. Each MATa/MATα rec/rec diploid is deficient in mitotic single site gene conversion, intragenic recombination, intergenic recombination and sporulation at the restrictive temperature (36°C). The rec1-1 mutation also confers conditional enhanced sensitivity to the killing effects of X-rays. The rec1-1 and rec3-1 mutations have been mapped to chromosome VII. The rec1-1, rec3-1 and rec4-1 mutations exhibit complementation at 36°C for both mitotic recombination and sporulation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 111 (1971), S. 297-299 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Diploid monohybrids of adenine 8 alleles were constructed to permit visual detection of meiotic gene conversion. In addition to the 3+:1 m and 1+:3 m tetrads routinely encountered, aberrant segregations comparable to the 5+:3 m and 3+:5 m patterns detected in octad ascomycetes were observed. These latter types are tetrads bearing ascospores which give rise to sectored ascosporal colonies.
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