The Active Mechanism of Nucleosome Depletion by Poly(dA:dT) Tracts In Vivo

Poly(dA:dT) tracts cause nucleosome depletion in many species, e.g., at promoters and replication origins. Their intrinsic biophysical sequence properties make them stiff and unfavorable for nucleosome assembly, as probed by in vitro nucleosome reconstitution. The mere correlation between nucleosome depletion over poly(dA:dT) tracts in in vitro reconstituted and in in vivo chromatin inspired an intrinsic nucleosome exclusion mechanism in vivo that is based only on DNA and histone properties. However, we compile here published and new evidence that this correlation does not reflect mechanistic causation. (1) Nucleosome depletion over poly(dA:dT) in vivo is not universal, e.g., very weak in S. pombe. (2) The energy penalty for incorporating poly(dA:dT) tracts into nucleosomes is modest (<10%) relative to ATP hydrolysis energy abundantly invested by chromatin remodelers. (3) Nucleosome depletion over poly(dA:dT) is much stronger in vivo than in vitro if monitored without MNase and (4) actively maintained in vivo. (5) S. cerevisiae promoters evolved a strand-biased poly(dA) versus poly(dT) distribution. (6) Nucleosome depletion over poly(dA) is directional in vivo. (7) The ATP dependent chromatin remodeler RSC preferentially and directionally displaces nucleosomes towards 5’ of poly(dA). Especially distribution strand bias and displacement directionality would not be expected for an intrinsic mechanism. Together, this argues for an in vivo mechanism where active and species-specific read out of intrinsic sequence properties, e.g., by remodelers, shapes nucleosome organization.

The Active Rather than Intrinsic Mechanism of Nucleosome Depletion by Poly(dA:dT) Tracts

Poly(dA:dT) tracts cause nucleosome depletion in many species, e.g., at promoters and replication origins. Their intrinsic biophysical sequence properties make them stiff and unfavorable for nucleosome assembly, as probed by in vitro nucleosome reconstitution. The mere correlation between nucleosome depletion over poly(dA:dT) tracts in vitro and in vivo inspired an intrinsic nucleosome exclusion mechanism in vivo. However, we compile here published and new evidence that this correlation does not reflect mechanistic causation. 1) Nucleosome depletion over poly(dA:dT) in vivo is not universal, e.g., very weak in S. pombe. 2) The energy penalty for incorporating poly(dA:dT) tracts into nucleosomes is modest (&lt;10%) relative to ATP hydrolysis energy abundantly invested by chromatin remodelers. 3) Nucleosome depletion over poly(dA:dT) is much stronger in vivo than in vitro if monitored without MNase and 4) actively maintained in vivo. 5) S. cerevisiae promoters evolved a biased poly(dA) versus poly(dT) distribution. 6) Nucleosome depletion over poly(dA) is directional in vivo. 7) The ATP dependent chromatin remodeler RSC preferentially and directionally displaces nucleosomes towards 5&rsquo; of poly(dA). Especially bias and directionality would not be expected for an intrinsic mechanism. Together, this argues for a mechanism where active and species-specific read out of intrinsic sequence properties, e.g., by remodelers, shapes nucleosome occupancy.

Distribution and Dispersion of Heavy Metals in the Rock–soil–moss System in Areas Covered by Black Shale in the Southeast of Guizhou Province, China

Black shales are easily exposed duo to human activities such as mining, road construction, and shale gas development, which results in several environmental issues including heavy metals (HMs) pollution, soil erosion and the destruction of vegetation. Moss are widely used to monitor metal pollution in the atmosphere, but few studies on the distribution and dispersion of HMs in the rock – soil – moss system are available. Here, mosses (P. flexuosa Harv), growing soils, and corresponding parent rocks were collected from black shale areas. After appropriate pretreatment, samples were analyzed for multiple elements concentration by ICP-AES and ICP-MS. The results show that black shales parent rocks have elevated HMs concentration, and act as a source of multiple metals. Soil significantly inherit and accumulate heavy metals released from black shale. Significant positive correlations between HMs in P. flexuosa Harv and the growing soils indicate that HMs are mainly originating from geological source rather than atmospheric deposition. Compared with other elements, only the transfer factor (TF) of Cd is greater than 1, the normal functioning of mineral elements (K and Zn) absorption and transportation may contribute to its high tolerance to Cd. Finally, both the BCF and TF for most HMs in P. flexuosa Harv are less than 1, indicated that it has a tolerance and exclusion mechanism for these metals. Therefore, the luxuriant and spontaneous growth of P. flexuosa Harv could be used as a phytostabilization pioneer plant in the black shale outcrop where vascular plants are rare.

DETERMINING THE LENGMUR COEFFICIENT OF THE FILTRATION PROBLEM

Filtration of suspension in a porous medium is actual in the construction of tunnels and underground structures. A model of deep bed filtration with size-exclusion mechanism of particle capture is considered. The inverse filtration problem - finding the Langmuir coefficient from a given concentration of suspended particles at the porous medium outlet is solved using the asymptotic solution near the concentrations front. The Langmuir coefficient constants are obtained by the least squares method from the condition of best approximation of the asymptotics to exact solution. It is shown that the calculated parameters are close to the coefficients of the model, and the asymptotics well approximates the exact solution

Social Exclusion in Health and Social Services Offered to Minority Patients: Do Racialization and Racism Play Roles?

Cultural and ethnic differences stemming from migration are a source of social exclusion in old age. This topic is of concern in part because an increased migration flow coupled with growing anti-immigrants sentiments in much of the Western world can ignite social exclusion mechanisms even when unintended. Given these trends, we ask whether racism figures in research on ethno-cultural and racial older minorities. Thus, based on a scoping review of peer-reviewed articles published between 1998-2017 (n=336), this presentation asks if, and how, racialization and racism inform this research. In answering these questions, this presentation will argue that the role that racism plays as a social exclusion mechanism that affects older ethnic and racial minorities needs to be studied in a systematic fashion. Part of a symposium sponsored by the International Aging and Migration Interest Group.

Entropic-Based Separation of Diastereomers: Size-Exclusion Chromatography with Online Viscometry and Refractometry Detection for Analysis of Blends of Mannose and Galactose Methyl-α-pyranosides at “Ideal” Size-Exclusion Conditions

The separation of carbohydrate diastereomers by an ideal size-exclusion mechanism, i.e., in the absence of enthalpic contributions to the separation, can be considered one of the grand challenges in chromatography: Can a difference in the location of a single axial hydroxy group on a pyranose ring (e.g., the axial OH being located on carbon 2 versus on carbon 4 of the ring) sufficiently affect the solution conformational entropy of a monosaccharide in a manner which allows for members of a diastereomeric pair to be separated from each other by size-exclusion chromatography (SEC)? Previous attempts at answering this question, for aqueous solutions, have been thwarted by the mutarotation of sugars in water. Here, the matter is addressed by employing the non-mutarotating methyl-α-pyranosides of d-mannose and d-galactose. We show for the first time, using SEC columns, the entropically driven separation of members of this diastereomeric pair, at a resolution of 1.2–1.3 and with only a 0.4–1% change in solute distribution coefficient over a 25 °C range, thereby demonstrating the ideality of the separation. It is also shown how the newest generation of online viscometer allows for improved sensitivity, thereby extending the range of this so-called molar-mass-sensitive detector into the monomeric regime. Detector multidimensionality is showcased via the synergism of online viscometry and refractometry, which combine to measure the intrinsic viscosity and viscometric radius of the sugars continually across the elution profiles of each diastereomer, methyl-α-d-mannopyranoside and methyl-α-d-galactopyranoside.