Ion-beam-induced amorphization and order-disorder transition in the murataite structure

Murataite (A3B6C2O22−x/2,F3m)(A3B6C2O22−x∕2,F4¯3m), a derivative of an anion-deficient fluorite structure, has been synthesized as different polytypes as a result of cation ordering. Ion-beam-induced amorphization has been investigated by 1-MeV1-MeV Kr2+Kr2+ ion irradiation with in situ transmission electron microscopy. The critical amorphization dose was determined as a function of temperature and the degree of structural disordering. A lower critical amorphization temperature ( ∼ 860 K)(∼860K) was obtained for the disordered murataite as compared with that of the murataite superstructure (930 to 1060 K)(930to1060K). An ion-beam-induced ordered murataite to a disordered fluorite transition occurred in the murataite superstructure, similar to that observed in the closely related pyrochlore structure-type, A2B2O7A2B2O7. The ion-beam-induced defect fluorite structure is more energetically stable in the murataite structure with a higher degree of structural disordering, as compared with the murataite superstructure. This suggests that the degree of intrinsic structural disorder has a significant effect on the energetics of structural disordering process; this affects the tendency toward the order-disorder structural transition for fluorite-related compounds and their response to ion-beam-induced amorphization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87577/2/113536_1.pd

The Effect of Waste Loading and Glass Structural Factors on Structure and Chemical Durability of SB2 and SB4 SRS Waste Glasses -11397

ABSTRACT Glassy materials simulating vitrified high-Na/Fe (Sludge Batch 2 -SB2) and high-Na/Fe/Al (Sludge Batch 4 -SB4) Savannah River Site high level wastes (HLW) were produced in a resistive furnace and 236 and 418 mm inner diameter cold crucibles. The effect of waste loading (WL) and glass structural factors (degree of connectedness of glass network, metal oxides to boron oxide ratios) on chemical durability of glassy materials was studied

Specific features of the substitution of Fe3+ impurity ions for Zr4+ in NaZr2(PO4)3 single crystals

The EPR spectra of Fe3+ impurity ions in NaZr 2(PO4)3 single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe3+ impurity ions substitute for Zr4+ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B4 and the crystal-field tensor V44 4 depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed. © 2005 Pleiades Publishing, Inc

Epigenetic Engineering of Ribosomal RNA Genes Enhances Protein Production

Selection of mammalian high-producer cell lines remains a major challenge for the biopharmaceutical manufacturing industry. Ribosomal RNA (rRNA) genes encode the major component of the ribosome but many rRNA gene copies are not transcribed [1]–[5] due to epigenetic silencing by the nucleolar remodelling complex (NoRC) [6], which may limit the cell's full production capacity. Here we show that the knockdown of TIP5, a subunit of NoRC, decreases the number of silent rRNA genes, upregulates rRNA transcription, enhances ribosome synthesis and increases production of recombinant proteins. However, general enhancement of rRNA transcription rate did not stimulate protein synthesis. Our data demonstrates that the number of transcriptionally competent rRNA genes limits efficient ribosome synthesis. Epigenetic engineering of ribosomal RNA genes offers new possibilities for improving biopharmaceutical manufacturing and provides novel insights into the complex regulatory network which governs the translation machinery in normal cellular processes as well as in pathological conditions like cancer

Nucleosomes in gene regulation: theoretical approaches

This work reviews current theoretical approaches of biophysics and bioinformatics for the description of nucleosome arrangements in chromatin and transcription factor binding to nucleosomal organized DNA. The role of nucleosomes in gene regulation is discussed from molecular-mechanistic and biological point of view. In addition to classical problems of this field, actual questions of epigenetic regulation are discussed. The authors selected for discussion what seem to be the most interesting concepts and hypotheses. Mathematical approaches are described in a simplified language to attract attention to the most important directions of this field

The Chromatin Remodelling Complex B-WICH Changes the Chromatin Structure and Recruits Histone Acetyl-Transferases to Active rRNA Genes

The chromatin remodelling complex B-WICH, which comprises the William syndrome transcription factor (WSTF), SNF2h, and nuclear myosin 1 (NM1), is involved in regulating rDNA transcription, and SiRNA silencing of WSTF leads to a reduced level of 45S pre-rRNA. The mechanism behind the action of B-WICH is unclear. Here, we show that the B-WICH complex affects the chromatin structure and that silencing of the WSTF protein results in a compaction of the chromatin structure over a 200 basepair region at the rRNA promoter. WSTF knock down does not show an effect on the binding of the rRNA-specific enhancer and chromatin protein UBF, which contributes to the chromatin structure at active genes. Instead, WSTF knock down results in a reduced level of acetylated H3-Ac, in particular H3K9-Ac, at the promoter and along the gene. The association of the histone acetyl-transferases PCAF, p300 and GCN5 with the promoter is reduced in WSTF knock down cells, whereas the association of the histone acetyl-transferase MOF is retained. A low level of H3-Ac was also found in growing cells, but here histone acetyl-transferases were present at the rDNA promoter. We propose that the B-WICH complex remodels the chromatin structure at actively transcribed rRNA genes, and this allows for the association of specific histone acetyl-transferases