Electronic structure and properties of (TiZrNbCu)_1-xNi_x high entropy amorphous alloys

A comprehensive study of selected properties of four (TiZrNbCu)_1-xNi_x (x \le 0.25) amorphous high entropy alloys (a-HEA) has been performed. The samples were ribbons about 20 \mum thick and their fully amorphous state was verified by X-ray diffraction and thermal analysis. The surface morphology, precise composition and the distribution of components were studied with a Scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment. The properties selected were the melting temperature (T_m), the low temperature specific heat (LTSH), the magnetic susceptibility \chi_exp and the Young^,s modulus (E). Whereas LTSH and \chi_exp were measured for the as-cast samples, E was measured both for as-cast samples and relaxed samples (after a short anneal close to the glass transition temperature). The LTSH showed that the electronic density of states at the Fermi level, N_0(E_F), decreases with increasing x, whereas the Debye temperature (\theta_D) increases with x. This is similar to what is observed in binary and ternary amorphous alloys of early transition metals (TE) with late transition metals (TL) and indicates that N_0(E_F) is dominated by the d-electrons of the TE. The LTSH also showed the absence of superconductivity down to 1.8K and indicated the emergence of the Boson peak above 4K in all alloys.The free-electron like paramagnetic contribution to \chi_exp also decreases with x, whereas E, like \theta_D, increases with x, indicating enhanced interatomic bonding on addition of Ni. The applicability of the rule of mixtures to these and other similar HEAs is briefly discussed

PTB and <i>let-7</i> miRNA contribute together to regulate gene expression in <i>C. elegans</i>.

<p>(A) Synchronized L1 animals were placed at semi-permissive temperature (20°C) and adult animals were scored after seventieth-two hours. The animal sterility observed in the population is caused by either a vulval bursting at the L4-adult transition or by a severe gonadal defect. Error bars represent the 95% confidence interval from independent experiments (n) where between 20 and 40 animals have been scored. ***: p<0.0001 (B) <i>let-7</i> level remained unchanged in the <i>let-7ts</i>/<i>ptb-1</i> animals. RNAs were purified from the indicated genotypes and probed for <i>let-7</i> and U6 RNAs. The amount of RNA was used for Northern blotting is indicated on the top of the panel and the U6/<i>let-7</i> ratios are presented at the bottom of the panel.</p

PTB alters Ago2 association of mRNAs in HeLa cells.

<p>(A) PTB and nPTB was simultaneously knocked down in triplicates in HeLa cells and Ago2 was immunoprecipitated from control and PTB/nPTB siRNA transfected cells. PTB, nPTB, Ago2 expression was followed by Western hybridization. Tubulin was used as loading control. *: non-specific band detected with the nPTB antibody. (B–F) q-PCR analysis of mRNAs which association with Ago2 is modulated by PTB. RNAs were isolated from control and PTB/nPTB siRNA transfected cells and from Ago2 IPs obtained from the same cells. RNAs were quantified and normalized with GAPDH RNA. The data show the relative abundance of the normalized RNAs compared to the control siRNA transfected cells and the Ago2 IP from the same cells. Error bars represent the standard deviation of three independent experiments (A). *: p<0.05, **: p<0.001.</p

Affinity purification of <i>let-7</i> associated complexes.

<p>(A) Biotinylated 2-<i>O</i>-methylated oligos used in this study. Sequences highlighted with red are complementary to <i>let-7a</i>. Blue nucleotides indicate changes generated from the original <i>let-7</i> oligo. (B) Northern hybridization (top panel) and Western blot (bottom panel) show that <i>let-7</i> oligo specifically purifies <i>let-7</i> miRNA and hAgo2 protein. sup.: supernatant; c and cont.: control oligo. (C) Proteins co-purify with <i>let-7</i> oligo. Right and left panels show the results of the independent affinity purifications. Proteins that are specifically pulled down with the <i>let-7</i> oligo are labeled next to the stained gels.</p

PTB association with the <i>let-7</i> bead depends of the <i>let-7</i> seed complementary sequences.

<p>(A) <i>let-7</i> seed mutant oligo could not inhibit <i>let-7</i> mediated gene repression. Renilla luciferase expressing plasmid containing a part of the 3′ UTR of human HMGA2 that carries four <i>let-7</i> target sites were transfected into HeLa cells together with Firefly expressing plasmid, as internal control, and the indicated 2′-<i>O</i>-methyl oligos. The graph shows the result of the dual-luciferase assay normalized to the control oligo. The error bars represent the standard error of three experiments. (B) <i>let-7</i>, hAgo2 and PTB are sensitive to the presence of the seed sequence of the <i>let-7</i> oligo. The quantity of <i>let-7</i> miRNA associated with the indicated oligos was quantified using Northern hybridization and normalized to the amount of miRNA pulled down with the wild-type <i>let-7</i> oligo. The presences of hAgo2 and PTB on the indicated beads were monitored by Western hybridization. (C) PTB association with the <i>let-7</i> column does not depend on the presence of the canonical PTB site in the oligo. Affinity purifications were carried out with the indicated oligos and the association of miRNAs, hAgo2 and PTB with these oligos was monitored by Northern hybridization and Western blotting. sup.: supernatant.</p

PTB is associated with hAgo2 and <i>let-7</i> miRNA.

<p>Endogenous PTB in Hela cells (A), PTB fused with GFP in HeLa cells (B) and stably expressed GFP::PTB in U2OS cells (C) co-purify with endogenous hAgo2 and <i>let-7</i>. Immunoprecipitations (IP) were carried out with the indicated antibodies. The bound fractions were assayed for hAgo2 and PTB with western blotting (top panels) and for <i>let-7</i> with Northern hybridization (bottom panels). (D) PTB association with Ago2 is mediated by RNA. IPs were carried out with antibodies against GFP and PTB. The parts of the bound fraction were subjected to RNase treatment and the supernatants of the RNAse treated beads and the remaining bound fractions were assayed for hAgo2 and PTB by Western blotting.</p

nPTB could also be associated with miRISC.

<p>(A) The knock down of PTB results in the increase of nPTB expression in HeLa cells. PTB was knock down with specific siRNA and PTB and nPTB levels were monitored with Western blotting. Tubulin was used as a loading control. *: non-specific hybridization visualized by he nPTB abtibody. (B) nPTB is associated with miRNA. XR tagged nPTB was overexpressed and IP was carried out with antibody recognizing XR. The efficiency of the IP was checked with Western blotting using XR and nPTB antibodies. RNA was purified from the immunoprecipitates and assayed for the presence of <i>let-7</i> using Northern blotting. c: empty bead.</p