Electrical Resistance of Copper-Gold Alloys at Low Temperatures

Electrical resistance of the copper-gold alloys containing 5.0_6, 24.1, 25.0_7, 50.8, 74.0 and 75.0_6 at. % gold was measured in the range from liquid helium to room temperature in the annealed and quenched states. It was established that the residual resistance of the 75.0_6 per cent alloy is lower in the ordered state than in the disordered one, and that the ratios of the residual resistance to the ice point resistance are 0.699 and 0.800 for the ordered and disordered states, respectively. Also it was found for the 74.0 per cent alloy that the residual resistance of the partly ordered state is higher than that of the disordered state. The Debye temperatures of the alloys were evaluated by using the Gruneisen formula. 185°and 160°K were obtained for the 75.0_6 per cent alloy in the ordered and disordered states, respectively. A resistance minimum of the magnitude of 0.01 μΩ-cm was found in the neighborhood of 13°K for the 25.0_7 per cent alloy. Such a minimum seems to be little affected by the degree of order, and was thought to be due to the presence of small amounts of certain impurities. This view was supported by an appearance of more distinct minimum near 19°K for the 23.5_7 per cent alloy containing 0.16 per cent iron as an impurity

Structural basis for the sequence-specific RNA-recognition mechanism of human CUG-BP1 RRM3

The CUG-binding protein 1 (CUG-BP1) is a member of the CUG-BP1 and ETR-like factors (CELF) family or the Bruno-like family and is involved in the control of splicing, translation and mRNA degradation. Several target RNA sequences of CUG-BP1 have been predicted, such as the CUG triplet repeat, the GU-rich sequences and the AU-rich element of nuclear pre-mRNAs and/or cytoplasmic mRNA. CUG-BP1 has three RNA-recognition motifs (RRMs), among which the third RRM (RRM3) can bind to the target RNAs on its own. In this study, we solved the solution structure of the CUG-BP1 RRM3 by hetero-nuclear NMR spectroscopy. The CUG-BP1 RRM3 exhibited a noncanonical RRM fold, with the four-stranded b-sheet surface tightly associated with the N-terminal extension. Furthermore, we determined the solution structure of the CUG-BP1 RRM3 in the complex with (UG)3 RNA, and discovered that the UGU trinucleotide is specifically recognized through extensive stacking interactions and hydrogen bonds within the pocket formed by the b-sheet surface and the N-terminal extension. This study revealed the unique mechanism that enables the CUG-BP1 RRM3 to discriminate the short RNA segment from other sequences, thus providing the molecular basis for the comprehension of the role of the RRM3s in the CELF/Bruno-like family