3,803 research outputs found
QUASI FROBENIUS LIE ALGEBRAS CONSTRUCTION OF N=4 SUPERCONFORMAL FIELD THEORIES
Manin triple construction of N=4 superconformal field theories is considered.
The correspondence between quasi Frobenius finite-dimensional Lie algebras and
N=4 superconformal field theories is established.Comment: 20 pages, PLAINTE
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Communication between distinct subunit interfaces of the cohesin complex promotes its topological entrapment of DNA.
Cohesin mediates higher order chromosome structure. Its biological activities require topological entrapment of DNA within a lumen(s) formed by cohesin subunits. The reversible dissociation of cohesins Smc3p and Mcd1p subunits is postulated to form a regulated gate that allows DNA entry and exit into the lumen. We assessed gate-independent functions of this interface in yeast using a fusion protein that joins Smc3p to Mcd1p. We show that in vivo all the regulators of cohesin promote DNA binding of cohesin by mechanisms independent of opening this gate. Furthermore, we show that this interface has a gate-independent activity essential for cohesin to bind chromosomes. We propose that this interface regulates DNA entrapment by controlling the opening and closing of one or more distal interfaces formed by cohesin subunits, likely by inducing a conformation change in cohesin. Furthermore, cohesin regulators modulate the interface to control both DNA entrapment and cohesin functions after DNA binding
Use of a distant reporter group as evidence for a conformational change in a sensory receptor
A highly sensitive method for demonstrating ligand-induced conformational changes in protein molecules in solution is described. The method utilizes an environmentally sensitive reporter group that is known to be distant from the active site. In the present application a conformational change is demonstrated in the galactose receptor of Salmonella typhimurium, involved in bacterial sensing and transport, by means of an extrinsic fluorophore, 5-iodoacetamidofluorescein, attached at a single methionine residue, and the intrinsic tryptophan fluorophore. Binding of the ligand galactose perturbs the microenvironment of both the fluorescein and tryptophan, as shown by both spectral and potassium iodide quenching changes. The distance between the two dyes is established by fluorescence energy transfer methods to be 41 ± 10 angstrom. Since only one molecule of galactose binds per molecule of receptor and since the galactose molecule is only about 5 angstrom in length, changes at one of these sites reflect the result of an indirect effect. Hence, there must be a ligand-induced conformational change that is propagated a minimum of 30 angstrom through the receptor molecule
Training BIG to move faster: the application of the speed–amplitude relation as a rehabilitation strategy for people with Parkinson’s disease
We have used the phenomenon that speed increases with movement amplitude as a rehabilitation strategy. We tested the hypothesis that the generalized training of amplitude in the limb motor system may reduce bradykinesia and hypokinesia in the upper and lower limbs in subjects with Parkinson’s disease (PD) across disease severity (Stage I, n=6; Stage II, n=7; Stage III, n=5). While studies have separately examined the relationship of amplitude to speed in reaching and gait, the same study has not reported the relationship for both limb systems. Moreover, the rehabilitation intervention, Training BIG, is unique in that it applies well-established treatment concepts from a proven treatment for the speech motor system in PD [Lee Silverman Voice Treatment (LSVT®)] to the limb motor system. Subjects (n=18) participated in intense practice (1-h sessions/4× week/4 weeks) of large amplitude movements involving the whole body (i.e., head, arm, trunk, and leg) while focusing on the sensory awareness of “movement bigness.” Testing procedures were designed to demonstrate the transfer of generalized amplitude practice to speed improvements during functional “untrained” tasks in “uncued” conditions with blinded testers. After therapy, the subjects significantly increased their speed of reaching and gait for the preferred speed condition. This effect was greater when the severity of the disease was less. The results support further application and efficacy studies of Training BIG. Amplitude-based behavioral intervention in people with PD appears to be a simple target that may be applied in different contexts for multiple tasks and results in improved speed–amplitude scaling relations across the upper and lower limbs
Chromosomal Addresses of the Cohesin Component Mcd1p
We identified the chromosomal addresses of a cohesin subunit, Mcd1p, in vivo by chromatin immunoprecipitation coupled with high resolution PCR-based chromosomal walking. The mapping of new Mcd1p-binding sites (cohesin-associated regions [CARs]) in single-copy sequences of several chromosomes establish their spacing (∼9 kb), their sequestration to intergenic regions, and their association with AT-rich sequences as general genomic properties of CARs. We show that cohesins are not excluded from telomere proximal regions, and the enrichment of cohesins at the centromere at mitosis reflects de novo loading. The average size of a CAR is 0.8–1.0 kb. They lie at the boundaries of transcriptionally silenced regions, suggesting they play a direct role in defining the silent chromatin domain. Finally, we identify CARs in tandem (rDNA) and interspersed repetitive DNA (Ty2 and subtelomeric repeats). Each 9-kb rDNA repeat has a single CAR proximal to the 5S gene. Thus, the periodicity of CARs in single-copy regions and the rDNA repeats is conserved. The presence and spacing of CARs in repetitive DNA has important implications for genomic stability and chromosome packaging/condensation
Genetic drift at expanding frontiers promotes gene segregation
Competition between random genetic drift and natural selection plays a
central role in evolution: Whereas non-beneficial mutations often prevail in
small populations by chance, mutations that sweep through large populations
typically confer a selective advantage. Here, however, we observe chance
effects during range expansions that dramatically alter the gene pool even in
large microbial populations. Initially well-mixed populations of two
fluorescently labeled strains of Escherichia coli develop well-defined,
sector-like regions with fractal boundaries in expanding colonies. The
formation of these regions is driven by random fluctuations that originate in a
thin band of pioneers at the expanding frontier. A comparison of bacterial and
yeast colonies (Saccharomyces cerevisiae) suggests that this large-scale
genetic sectoring is a generic phenomenon that may provide a detectable
footprint of past range expansions.Comment: Please visit http://www.pnas.org/content/104/50/19926.abstract for
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Meiotic condensin is required for proper chromosome compaction, SC assembly, and resolution of recombination-dependent chromosome linkages
Condensin is an evolutionarily conserved protein complex that helps mediate chromosome condensation and segregation in mitotic cells. Here, we show that condensin has two activities that contribute to meiotic chromosome condensation in Saccharomyces cerevisiae. One activity, common to mitosis, helps mediate axial length compaction. A second activity promotes chromosome individualization with the help of Red1 and Hop1, two meiotic specific components of axial elements. Like Red1 and Hop1, condensin is also required for efficient homologue pairing and proper processing of double strand breaks. Consistent with these functional links condensin is necessary for proper chromosomal localization of Red1 and Hop1 and the subsequent assembly of the synaptonemal complex. Finally, condensin has a Red1/Hop1-independent role in the resolution of recombination-dependent linkages between homologues in meiosis I. The existence of distinct meiotic activities of condensin (axial compaction, individualization, and resolution of recombination-dependent links) provides an important framework to understand condensin's role in both meiotic and mitotic chromosome structure and function
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