Investigating the reactivity of an abasic lesion within nucleosomes and probing the interactions between histone tails and nucleosomal DNA in nucleosome core particles

DNA lesions are the source of the cytotoxicity of various antitumor reagents and γ-radiolysis. Studying the reactivity of these lesions and their effects in biological processes may provide the chemical basis for anticancer treatment and shed light on the rational design of novel drugs. The oxidized abasic lesion 5’-(2-phosphoryl-1,4-dioxobutane) (DOB) is produced concomitantly with a strand break via C5'-hydrogen atom abstraction by a variety of DNA-damaging agents. Herein, we report that the reactivity of DOB is distinct in nucleosomes from that in free DNA. DOB undergoes cleavage at a significantly higher rate in NCPs compared to free DNA, exhibiting a half-life of 8.5-16.8 min depending upon the sites in which DOB is generated. The rate constant of DOB decomposition is faster than its expected rate of repair in cells. DOB decomposition results in a pyrrolone modification of the histone tail. Furthermore, DOB decomposition within the linker DNA that connects two adjacent nucleosomes is also accelerated, albeit to a lesser extent than that within NCPs. The pyrrolone modification was observed in the histone H3 as a result of the interactions of the H3 tail interacting with the lesion in the linker region. The unnatural modification resulting from reaction with the DNA lesion may have profound biological consequences. The interactions between histone tails and nucleosomal DNA play significant roles in chromatin assembly and the regulation of gene expression. Recent studies including the one presented above revealed that residues on the N-terminal tails of histone proteins are intensively involved in catalyzing the decomposition of DNA lesions at specific sites within NCPs. Despite their importance, such interactions are not well defined due to the mobility of histone tails and the transient nature of the interactions. To gain insight into such interactions, we developed a new DNA-protein cross-linking (DPC) method by taking advantage of the reaction between a modified electrophilic nucleotide (2) and the nucleophilic residues in histone tails. Phenyl selenide 1 rapidly produces 2 upon mild oxidation, which reacts with nucleophilic amino acid side chains. The facile reaction and high DPC yields produced from 2 enabled both product and kinetic analysis, which ranked the contributions by individual and/or groups of amino acids (His18 > Lys16 > Lys20 ~ Lys8,12 > Lys5) that react with 2 at position 89 within the NCP, a hot spot for DNA damage. In addition, photolysis of 1 produced ICLs in free DNA and NCPs. The reexamination of photochemistry of 1 revealed that a carbocation intermediate (19) is responsible for the DNA ICL formation

Career Experience and Executive Performance: Evidence from Former Equity Research Analysts

This study examines CEOs and CFOs who have prior work experience as equity research analysts. Consistent with backgrounds in forecasting and valuation, we find these executives provide earnings guidance that is more accurate than that of other executives, and their M&A transactions generate significantly higher announcement returns. For available CEOs and CFOs, we examine their track records as research analysts with respect to forecasting accuracy and stock recommendation profitability. We find a positive association between a record of past forecasting accuracy and more accurate earnings guidance, as well as a positive association between past stock recommendation profitability and M&A announcement returns. Beyond these traits, we find these executives provide greater certainty in their answers to analysts during conference calls, especially when answering forward-looking questions. Finally, these executives’ firms exhibit superior accounting and stock return performance. Overall, our evidence suggests early career skill sets can shape top executive performance outcomes

Dissecting the Genetic Basis Underlying Combining Ability of Plant Height Related Traits in Maize

Maize plant height related traits including plant height, ear height, and internode number are tightly linked with biomass, planting density, and grain yield in the field. Previous studies have focused on understanding the genetic basis of plant architecture traits per se, but the genetic basis of combining ability remains poorly understood. In this study, 328 recombinant inbred lines were inter-group crossed with two testers to produce 656 hybrids using the North Carolina II mating design. Both of the parental lines and hybrids were evaluated in two summer maize-growing regions of China in 2015 and 2016. QTL mapping highlighted that 7 out of 16 QTL detected for RILs per se could be simultaneously detected for general combining ability (GCA) effects, suggesting that GCA effects and the traits were genetically controlled by different sets of loci. Among the 35 QTL identified for hybrid performance, 57.1% and 28.5% QTL overlapped with additive/GCA and non-additive/SCA effects, suggesting that the small percentage of hybrid variance due to SCA effects in our design. Two QTL hotspots, located on chromosomes 5 and 10 and including the qPH5-1 and qPH10 loci, were validated for plant height related traits by Ye478 derivatives. Notably, the qPH5-1 locus could simultaneously affect the RILs per se and GCA effects while the qPH10, a major QTL (PVE > 10%) with pleiotropic effects, only affected the GCA effects. These results provide evidence that more attention should be focused on loci that influence combining ability directly in maize hybrid breeding

Investigating the reactivity of an abasic lesion within nucleosomes and probing the interactions between histone tails and nucleosomal DNA in nucleosome core particles

DNA lesions are the source of the cytotoxicity of various antitumor reagents and γ-radiolysis. Studying the reactivity of these lesions and their effects in biological processes may provide the chemical basis for anticancer treatment and shed light on the rational design of novel drugs. The oxidized abasic lesion 5’-(2-phosphoryl-1,4-dioxobutane) (DOB) is produced concomitantly with a strand break via C5'-hydrogen atom abstraction by a variety of DNA-damaging agents. Herein, we report that the reactivity of DOB is distinct in nucleosomes from that in free DNA. DOB undergoes cleavage at a significantly higher rate in NCPs compared to free DNA, exhibiting a half-life of 8.5-16.8 min depending upon the sites in which DOB is generated. The rate constant of DOB decomposition is faster than its expected rate of repair in cells. DOB decomposition results in a pyrrolone modification of the histone tail. Furthermore, DOB decomposition within the linker DNA that connects two adjacent nucleosomes is also accelerated, albeit to a lesser extent than that within NCPs. The pyrrolone modification was observed in the histone H3 as a result of the interactions of the H3 tail interacting with the lesion in the linker region. The unnatural modification resulting from reaction with the DNA lesion may have profound biological consequences. The interactions between histone tails and nucleosomal DNA play significant roles in chromatin assembly and the regulation of gene expression. Recent studies including the one presented above revealed that residues on the N-terminal tails of histone proteins are intensively involved in catalyzing the decomposition of DNA lesions at specific sites within NCPs. Despite their importance, such interactions are not well defined due to the mobility of histone tails and the transient nature of the interactions. To gain insight into such interactions, we developed a new DNA-protein cross-linking (DPC) method by taking advantage of the reaction between a modified electrophilic nucleotide (2) and the nucleophilic residues in histone tails. Phenyl selenide 1 rapidly produces 2 upon mild oxidation, which reacts with nucleophilic amino acid side chains. The facile reaction and high DPC yields produced from 2 enabled both product and kinetic analysis, which ranked the contributions by individual and/or groups of amino acids (His18 > Lys16 > Lys20 ~ Lys8,12 > Lys5) that react with 2 at position 89 within the NCP, a hot spot for DNA damage. In addition, photolysis of 1 produced ICLs in free DNA and NCPs. The reexamination of photochemistry of 1 revealed that a carbocation intermediate (19) is responsible for the DNA ICL formation

Rapid Histone-Catalyzed DNA Lesion Excision and Accompanying Protein Modification in Nucleosomes and Nucleosome Core Particles

C5′-Hydrogen atoms are frequently abstracted during DNA oxidation. The oxidized abasic lesion 5′-(2-phosphoryl-1,4-dioxobutane) (DOB) is an electrophilic product of the C5′-radical. DOB is a potent irreversible inhibitor of DNA polymerase β, and forms interstrand cross-links in free DNA. We examined the reactivity of DOB within nucleosomes and nucleosome core particles (NCPs), the monomeric component of chromatin. Depending upon the position at which DOB is generated within a NCP, it is excised from nucleosomal DNA at a rate 275–1500-fold faster than that in free DNA. The half-life of DOB (7.0–16.8 min) in NCPs is shorter than any other abasic lesion. DOB’s lifetime in NCPs is also significantly shorter than the estimated lifetime of an abasic site within a cell, suggesting that the observed chemistry would occur intracellularly. Histones also catalyze DOB excision when the lesion is present in the DNA linker region of a nucleosome. Schiff-base formation between DOB and histone proteins is detected in nucleosomes and NCPs, resulting in pyrrolone formation at the lysine residues. The lysines modified by DOB are often post-translationally modified. Consequently, the histone modifications described herein could affect the regulation of gene expression and may provide a chemical basis for the cytotoxicity of the DNA damaging agents that produce this lesion

Environmental Resistance and Fatigue Behaviors of Epoxy/Nano-Boron Nitride Thermally Conductive Structural Film Adhesive Toughened by Polyphenoxy

The thermally conductive structural film adhesive not only carries large loads but also exhibits excellent heat-transfer performance, which has huge application prospects. Herein, a novel epoxy (Ep) thermally conductive structural film adhesive was prepared using polyphenoxy (PHO) as the toughening agent and film former, boron nitride (BN) nanosheets as the thermally conductive filler, and polyester fabric as the carrier. When the amount of PHO in the epoxy matrix was 30 phr and the content of nano-BN was 30 wt.% (Ep/PHO30/nBN30), the adhesive resin system showed good film-forming properties, thermal stability, and thermal conductivity. The glass transition temperature of Ep/PHO30/nBN30 was 215 °C, and the thermal conductivity was 209.5% higher than that of the pure epoxy resin. The Ep/PHO30/nBN30 film adhesive possessed excellent adhesion and peeling properties, and the double-lap shear strength at room temperature reached 36.69 MPa, which was 21.3% higher than that of pure epoxy resin. The double-lap shear strength reached 15.41 MPa at 150 °C, demonstrating excellent high temperature resistance. In addition, the Ep/PHO30/nBN30 film adhesive exhibited excellent heat-aging resistance, humidity, and medium resistance, and the shear strength retention rate after exposure to the complicated environment reached more than 90%. The structural film adhesive prepared showed excellent fatigue resistance in the dynamic load fatigue test, the double-lap shear strength still reached 35.55 MPa after 1,000,000 fatigue cycles, and the strength retention rate was 96.9%, showing excellent durability and fatigue resistance

Probing Interactions between Lysine Residues in Histone Tails and Nucleosomal DNA via Product and Kinetic Analysis

The histone proteins in nucleosome core particles are known to catalyze DNA cleavage at abasic and oxidized abasic sites, which are produced by antitumor antibiotics and as a consequence of other modalities of DNA damage. The lysine rich histone tails whose post-translational modifications regulate genetic expression in cells are mainly responsible for this chemistry. Cleavage at a C4′-oxidized abasic site (C4-AP) concomitantly results in modification of lysine residues in histone tails. Using LC-MS/MS, we demonstrate here that that Lys8, -12, -16, and -20 of histone H4 were modified when C4-AP was incorporated at a hot spot (superhelical location 1.5) for DNA damage within a nucleosome core particle. A new DNA–protein cross-linking method that provides a more quantitative analysis of individual amino acid reactivity is also described. DNA–protein cross-links were produced by an irreversible reaction between a nucleic acid electrophile that was produced following oxidatively induced rearrangement of a phenyl selenide derivative of thymidine (<b>3</b>) and nucleophilic residues within proteins. In addition to providing high yields of DNA–protein cross-links, kinetic analysis of the cross-linking reaction yielded rate constants that enabled ranking the contributions by individual or groups of amino acids. Cross-linking from <b>3</b> at superhelical location 1.5 revealed the following order of reactivity for the nucleophilic amino acids in the histone H4 tail: His18 > Lys16 > Lys20 ≈ Lys8, Lys12 > Lys5. Cross-linking via <b>3</b> will be generally useful for investigating DNA–protein interactions

Preparation of Novel Epoxy Resins Bearing Phthalazinone Moiety and Their Application as High-Temperature Adhesives

Most polymer-based adhesives exhibit some degree of degradation at temperatures above 200 &deg;C, and so there is a need for the development of adhesives that can be used at high temperatures. A series of poly(phthalazinone ether nitrile sulfone ketone)s terminated with epoxy (E-PPENSK) and amine (A-PPENSK) groups have been prepared, which have been used as precursors can be applied for high-temperature resistant epoxy adhesives. The structured of these E-PPENSK (epoxy resin) and A-PPENSK (curing agent) components have been characterized by 1H nuclear magnetic resonance (NMR) and Fourier transform&ndash;infrared spectroscopy (FT&ndash;IR) studies, with the effects of molecular weights and molar ratios on the gel content of their polymers being determined. Cured epoxy resins derived from E-PPENSK and A-PPENSK showed good thermal stability, with an optimal resin retaining 95% of its weight at 484 &deg;C, which gave a char yield of 62%. This adhesive was found to exhibit good mechanical strength, with a single-lap adhesive joint (A-3000/E-6000) exhibiting a shear strength of 48.7 MPa. Heating this adhesive at 450 &deg;C for 1 h afforded a polymer that still exhibited good shear strength of 17.8 MPa, indicating that these adhesives are potentially good candidates for high-temperature applications

PPESK-Modified Multi-Functional Epoxy Resin and Its Application to the Pultrusion of Carbon Fiber

Multi-functional epoxy resins are generally brittle due to their high crosslinking densities, which can limit their use for applications that require impact resistance. Pultruded poly(phthalazinone ether sulfone ketone) (PPESK)-modified epoxy resins were prepared and their curing behaviors, heat resistance properties, and viscosity changes investigated. The glass transition temperature of these resins was found to increase with increasing PPESK content; however, these values were still compatible with the pultrusion process. Little change in the tensile strength and elongation lengths at breaking point were observed for blended PPESK/multi-functional epoxy resin containing 4&ndash;6% PPESK, and its viscosity levels were still within the requirements of the pultrusion process. Carbon fiber/multi-functional epoxy resin/PPESK (CF/E/PPESK) composites were also prepared and their performance investigated. The bending radius of these PPSEK-modified composites could reach up to 55 D with no cracking or peeling observed in their surface layers. The fatigue frequency of the sinusoidal waveforms for the composite did not change after one million fatigue test cycles, meaning that a strength retention rate of &gt;90% was achieved. Therefore, this study describes a powerful approach for preparing toughened multi-functional epoxy resins that are well suited to pultrusion processes