The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Dean S. Dawson - One of the best experts on this subject based on the ideXlab platform.
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a zip1 separation of Function allele reveals that meiotic centromere Pairing drives meiotic segregation of achiasmate chromosomes in budding yeast
bioRxiv, 2018Co-Authors: Emily L Kurdzo, Hoa H Chuong, Dean S. DawsonAbstract:In meiosis I, homologous chromosomes segregate away from each other - the first of two rounds of chromosome segregation that allow the formation of haploid gametes. In prophase I, homologous partners become joined along their length by the synaptonemal complex (SC) and crossovers form between the homologs to generate links called chiasmata. The chiasmata allow the homologs to act as a single unit, called a bivalent, as the chromosomes attach to the microtubules that will ultimately pull them away from each other at anaphase I. Recent studies, in several organisms, have shown that when the SC disassembles at the end of prophase, residual SC proteins remain at the homologous centromeres providing an additional link between the homologs. In budding yeast, this centromere Pairing is correlated with improved segregation of the paired partners in anaphase. However, the causal relationship of prophase centromere Pairing and subsequent disjunction in anaphase has been difficult to demonstrate as has been the relationship between SC assembly and the assembly of the centromere Pairing apparatus. Here, a series of in-frame deletion mutants of the SC component Zip1 were used to address these questions. The identification of separation-of-Function alleles that disrupt centromere Pairing, but not SC assembly, have made it possible to demonstrate that centromere Pairing and SC assembly have mechanistically distinct features and that prophase centromere Pairing Function of Zip1 drives disjunction of the paired partners in anaphase I.
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A ZIP1 separation-of-Function allele reveals that centromere Pairing drives meiotic segregation of achiasmate chromosomes in budding yeast.
Public Library of Science (PLoS), 2018Co-Authors: Emily L Kurdzo, Hoa H Chuong, Jared M Evatt, Dean S. DawsonAbstract:In meiosis I, homologous chromosomes segregate away from each other-the first of two rounds of chromosome segregation that allow the formation of haploid gametes. In prophase I, homologous partners become joined along their length by the synaptonemal complex (SC) and crossovers form between the homologs to generate links called chiasmata. The chiasmata allow the homologs to act as a single unit, called a bivalent, as the chromosomes attach to the microtubules that will ultimately pull them away from each other at anaphase I. Recent studies, in several organisms, have shown that when the SC disassembles at the end of prophase, residual SC proteins remain at the homologous centromeres providing an additional link between the homologs. In budding yeast, this centromere Pairing is correlated with improved segregation of the paired partners in anaphase. However, the causal relationship of prophase centromere Pairing and subsequent disjunction in anaphase has been difficult to demonstrate as has been the relationship between SC assembly and the assembly of the centromere Pairing apparatus. Here, a series of in-frame deletion mutants of the SC component Zip1 were used to address these questions. The identification of a separation-of-Function allele that disrupts centromere Pairing, but not SC assembly, has made it possible to demonstrate that centromere Pairing and SC assembly have mechanistically distinct features and that the centromere Pairing Function of Zip1 drives disjunction of the paired partners in anaphase I
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Meiotic Centromere Coupling and Pairing Function by Two Separate Mechanisms in Saccharomyces cerevisiae.
Genetics, 2017Co-Authors: Emily L Kurdzo, David Obeso, Hoa Chuong, Dean S. DawsonAbstract:In meiosis I, chromosomes become paired with their homologous partners and then are pulled toward opposite poles of the spindle. In the budding yeast, Saccharomyces cerevisiae, in early meiotic prophase, centromeres are observed to associate in pairs in a homology-independent manner; a process called centromere coupling. Later, as homologous chromosomes align, their centromeres associate in a process called centromere Pairing. The synaptonemal complex protein Zip1 is necessary for both types of centromere association. We aimed to test the role of centromere coupling in modulating recombination at centromeres, and to test whether the two types of centromere associations depend upon the same sets of genes. The zip1-S75E mutation, which blocks centromere coupling but no other known Functions of Zip1, was used to show that in the absence of centromere coupling, centromere-proximal recombination was unchanged. Further, this mutation did not diminish centromere Pairing, demonstrating that these two processes have different genetic requirements. In addition, we tested other synaptonemal complex components, Ecm11 and Zip4, for their contributions to centromere Pairing. ECM11 was dispensable for centromere Pairing and segregation of achiasmate partner chromosomes; while ZIP4 was not required for centromere Pairing during pachytene, but was required for proper segregation of achiasmate chromosomes. These findings help differentiate the two mechanisms that allow centromeres to interact in meiotic prophase, and illustrate that centromere Pairing, which was previously shown to be necessary to ensure disjunction of achiasmate chromosomes, is not sufficient for ensuring their disjunction.
Masa-aki Ozaki - One of the best experts on this subject based on the ideXlab platform.
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A Spin Triplet Superconductor UPt$_3$
Journal of the Physical Society of Japan, 2012Co-Authors: Yasumasa Tsutsumi, Kazushige Machida, Tetsuo Ohmi, Masa-aki OzakiAbstract:Motivated by a recent angle-resolved thermal conductivity experiment that shows a twofold gap symmetry in the high-field and low-temperature C phase in the heavy-fermion superconductor UPt$_3$, we group-theoretically identify the Pairing Functions as $E_{1u}$ with the $f$-wave character for all the three phases. The Pairing Functions are consistent with the observation as well as with a variety of existing measurements. By using a microscopic quasi-classical Eilenberger equation with the identified triplet Pairing Function under applied fields, we performed detailed studies of the vortex structures for three phases, including the vortex lattice symmetry, the local density of states, and the internal field distribution. These quantities are directly measurable experimentally by SANS, STM/STS, and NMR, respectively. It is found that, in the B phase of low $H$ and low $T$, the double-core vortex is stabilized over a singular vortex. In the C phase, thermal conductivity data are analyzed to confirm the gap structure proposed. We also give detailed comparisons of various proposed pair Functions, concluding that the present scenario of $E_{1u}$ with the $f$-wave, which is an analogue to the triplet planar state, is better than the $E_{2u}$ or $E_{1g}$ scenario. Finally, we discuss the surface topological aspects of Majorana modes associated with the $E_{1u}^f$ state of planar like features.
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superconducting double transition in a heavy fermion material upt3
Physical Review Letters, 1991Co-Authors: Kazushige Machida, Masa-aki OzakiAbstract:To explain the field-independent phase diagrams observed in ${\mathrm{UPt}}_{3}$ a scenario based on a superconducting (SC) class belonging to the one-dimensional representation (1D-rep) with odd parity is proposed. The antiferromagnetic (AF) order lifts the spin-space degeneracy of the Pairing Function to split ${\mathit{T}}_{\mathit{c}}$. A nontrivial coupling of the two orderings, SC and AF, is derived and a Ginzburg-Landau theory is developed to examine the successive phase transitions. It is demonstrated that the present 1D-rep scenario is more consistent with various experiments on ${\mathrm{UPt}}_{3}$ than the previous 2D-rep scenario.
Emily L Kurdzo - One of the best experts on this subject based on the ideXlab platform.
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a zip1 separation of Function allele reveals that meiotic centromere Pairing drives meiotic segregation of achiasmate chromosomes in budding yeast
bioRxiv, 2018Co-Authors: Emily L Kurdzo, Hoa H Chuong, Dean S. DawsonAbstract:In meiosis I, homologous chromosomes segregate away from each other - the first of two rounds of chromosome segregation that allow the formation of haploid gametes. In prophase I, homologous partners become joined along their length by the synaptonemal complex (SC) and crossovers form between the homologs to generate links called chiasmata. The chiasmata allow the homologs to act as a single unit, called a bivalent, as the chromosomes attach to the microtubules that will ultimately pull them away from each other at anaphase I. Recent studies, in several organisms, have shown that when the SC disassembles at the end of prophase, residual SC proteins remain at the homologous centromeres providing an additional link between the homologs. In budding yeast, this centromere Pairing is correlated with improved segregation of the paired partners in anaphase. However, the causal relationship of prophase centromere Pairing and subsequent disjunction in anaphase has been difficult to demonstrate as has been the relationship between SC assembly and the assembly of the centromere Pairing apparatus. Here, a series of in-frame deletion mutants of the SC component Zip1 were used to address these questions. The identification of separation-of-Function alleles that disrupt centromere Pairing, but not SC assembly, have made it possible to demonstrate that centromere Pairing and SC assembly have mechanistically distinct features and that prophase centromere Pairing Function of Zip1 drives disjunction of the paired partners in anaphase I.
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A ZIP1 separation-of-Function allele reveals that centromere Pairing drives meiotic segregation of achiasmate chromosomes in budding yeast.
Public Library of Science (PLoS), 2018Co-Authors: Emily L Kurdzo, Hoa H Chuong, Jared M Evatt, Dean S. DawsonAbstract:In meiosis I, homologous chromosomes segregate away from each other-the first of two rounds of chromosome segregation that allow the formation of haploid gametes. In prophase I, homologous partners become joined along their length by the synaptonemal complex (SC) and crossovers form between the homologs to generate links called chiasmata. The chiasmata allow the homologs to act as a single unit, called a bivalent, as the chromosomes attach to the microtubules that will ultimately pull them away from each other at anaphase I. Recent studies, in several organisms, have shown that when the SC disassembles at the end of prophase, residual SC proteins remain at the homologous centromeres providing an additional link between the homologs. In budding yeast, this centromere Pairing is correlated with improved segregation of the paired partners in anaphase. However, the causal relationship of prophase centromere Pairing and subsequent disjunction in anaphase has been difficult to demonstrate as has been the relationship between SC assembly and the assembly of the centromere Pairing apparatus. Here, a series of in-frame deletion mutants of the SC component Zip1 were used to address these questions. The identification of a separation-of-Function allele that disrupts centromere Pairing, but not SC assembly, has made it possible to demonstrate that centromere Pairing and SC assembly have mechanistically distinct features and that the centromere Pairing Function of Zip1 drives disjunction of the paired partners in anaphase I
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Meiotic Centromere Coupling and Pairing Function by Two Separate Mechanisms in Saccharomyces cerevisiae.
Genetics, 2017Co-Authors: Emily L Kurdzo, David Obeso, Hoa Chuong, Dean S. DawsonAbstract:In meiosis I, chromosomes become paired with their homologous partners and then are pulled toward opposite poles of the spindle. In the budding yeast, Saccharomyces cerevisiae, in early meiotic prophase, centromeres are observed to associate in pairs in a homology-independent manner; a process called centromere coupling. Later, as homologous chromosomes align, their centromeres associate in a process called centromere Pairing. The synaptonemal complex protein Zip1 is necessary for both types of centromere association. We aimed to test the role of centromere coupling in modulating recombination at centromeres, and to test whether the two types of centromere associations depend upon the same sets of genes. The zip1-S75E mutation, which blocks centromere coupling but no other known Functions of Zip1, was used to show that in the absence of centromere coupling, centromere-proximal recombination was unchanged. Further, this mutation did not diminish centromere Pairing, demonstrating that these two processes have different genetic requirements. In addition, we tested other synaptonemal complex components, Ecm11 and Zip4, for their contributions to centromere Pairing. ECM11 was dispensable for centromere Pairing and segregation of achiasmate partner chromosomes; while ZIP4 was not required for centromere Pairing during pachytene, but was required for proper segregation of achiasmate chromosomes. These findings help differentiate the two mechanisms that allow centromeres to interact in meiotic prophase, and illustrate that centromere Pairing, which was previously shown to be necessary to ensure disjunction of achiasmate chromosomes, is not sufficient for ensuring their disjunction.
Kazushige Machida - One of the best experts on this subject based on the ideXlab platform.
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A Spin Triplet Superconductor UPt$_3$
Journal of the Physical Society of Japan, 2012Co-Authors: Yasumasa Tsutsumi, Kazushige Machida, Tetsuo Ohmi, Masa-aki OzakiAbstract:Motivated by a recent angle-resolved thermal conductivity experiment that shows a twofold gap symmetry in the high-field and low-temperature C phase in the heavy-fermion superconductor UPt$_3$, we group-theoretically identify the Pairing Functions as $E_{1u}$ with the $f$-wave character for all the three phases. The Pairing Functions are consistent with the observation as well as with a variety of existing measurements. By using a microscopic quasi-classical Eilenberger equation with the identified triplet Pairing Function under applied fields, we performed detailed studies of the vortex structures for three phases, including the vortex lattice symmetry, the local density of states, and the internal field distribution. These quantities are directly measurable experimentally by SANS, STM/STS, and NMR, respectively. It is found that, in the B phase of low $H$ and low $T$, the double-core vortex is stabilized over a singular vortex. In the C phase, thermal conductivity data are analyzed to confirm the gap structure proposed. We also give detailed comparisons of various proposed pair Functions, concluding that the present scenario of $E_{1u}$ with the $f$-wave, which is an analogue to the triplet planar state, is better than the $E_{2u}$ or $E_{1g}$ scenario. Finally, we discuss the surface topological aspects of Majorana modes associated with the $E_{1u}^f$ state of planar like features.
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Dispersive Gap Mode of Phonons in Anisotropic Superconductors
Journal of the Physical Society of Japan, 2003Co-Authors: Masanori Ichioka, Kazushige MachidaAbstract:We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the Pairing Function on the Fermi surface. When the sign of the Pairing Function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting Pairing Function.
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Orbital symmetry of a triplet Pairing in a heavy-fermion superconductor UPt3
Physica B-condensed Matter, 2000Co-Authors: Kazushige Machida, Tetsuo OhmiAbstract:Abstract It is demonstrated by calculating thermal conductivity and ultrasound attenuation that either non-unitary bipolar state d ( k )= b λ x ( k )+ i j λ y ( k ) or unitary planar state d ( k )= b λ x ( k )+ j λ y ( k ) ( j = a or c ) is most appropriate Pairing Function for UPt3, where a , b and c are orthogonal unit vectors. The orbital part ( λ x ( k ) , λ y ( k ) ) belongs to the two-dimensional E2u representation in D6h.
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superconducting double transition in a heavy fermion material upt3
Physical Review Letters, 1991Co-Authors: Kazushige Machida, Masa-aki OzakiAbstract:To explain the field-independent phase diagrams observed in ${\mathrm{UPt}}_{3}$ a scenario based on a superconducting (SC) class belonging to the one-dimensional representation (1D-rep) with odd parity is proposed. The antiferromagnetic (AF) order lifts the spin-space degeneracy of the Pairing Function to split ${\mathit{T}}_{\mathit{c}}$. A nontrivial coupling of the two orderings, SC and AF, is derived and a Ginzburg-Landau theory is developed to examine the successive phase transitions. It is demonstrated that the present 1D-rep scenario is more consistent with various experiments on ${\mathrm{UPt}}_{3}$ than the previous 2D-rep scenario.
Eric B. Kmiec - One of the best experts on this subject based on the ideXlab platform.
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Genetic re‐engineering of Saccharomyces cerevisiae RAD51 leads to a significant increase in the frequency of gene repair in vivo
Nucleic acids research, 2004Co-Authors: Li Liu, Katie Maguire, Eric B. KmiecAbstract:Oligonucleotides can be used to direct the alteration of single nucleotides in chromosomal genes in yeast. Rad51 protein appears to play a central role in catalyzing the reaction, most likely through its DNA Pairing Function. Here, we re-engineer the RAD51 gene in order to produce proteins bearing altered levels of known activities. Overexpression of wild-type ScRAD51 elevates the correction of an integrated, mutant hygromycin resistance gene approximately 3-fold. Overexpression of an altered RAD51 gene, which encodes a protein that has a higher affinity for ScRad54, enhances the targeting frequency nearly 100-fold. Another mutation which increases the affinity of Rad51 for DNA was also found to increase gene repair when overexpressed in the cell. Other mutations in the Rad51 protein, such as one that reduces interaction with Rad52, has little or no effect on the frequency of gene repair. These data provide the first evidence that the Rad51 protein can be modified so as to increase the frequency of gene repair in yeast.
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DNA Pairing is an important step in the process of targeted nucleotide exchange
Nucleic acids research, 2003Co-Authors: Miya D. Drury, Eric B. KmiecAbstract:Modified single-stranded DNA oligonucleotides can direct the repair of genetic mutations in yeast, plant and mammalian cells. The mechanism by which these molecules exert their effect is being elucidated, but the first phase is likely to involve the homologous alignment of the single strand with its complementary sequence in the target gene. In this study, we establish the importance of such DNA Pairing in facilitating the gene repair event. Oligonucleotide-directed repair occurs at a low frequency in an Escherichia coli strain (DH10B) lacking the RECA DNA Pairing Function. Repair activity can be rescued by using purified RecA protein to catalyze the assimilation of oligonucleotide vectors into a plasmid containing a mutant kanamycin resistance gene in vitro. Electroporation of the preformed complex into DH10B cells results in high levels of gene repair activity, evidenced by the appearance of kanamycin-resistant colonies. Gene repair is dependent on the formation of a double-displacement loop (double-D-loop), a recombination intermediate containing two single-stranded oligonucleotides hybridized to opposite strands of the plasmid at the site of the point mutation. The heightened level of stability of the double-D-loop enables it to serve as an active template for the DNA repair events. The data establish DNA Pairing and the formation of the double-D-loop as important first steps in the process of gene repair.
