Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5

With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.     

Global landscape of protein complexes in the yeast Saccharomyces cerevisiae

Identification of protein-protein interactions often provides insight into protein function, and many cellular processes are performed by stable protein complexes. We used tandem affinity purification to process 4,562 different tagged proteins of the yeast Saccharomyces cerevisiae. Each preparation was analysed by both matrix-assisted laser desorption/ionization-time of flight mass spectrometry and liquid chromatography tandem mass spectrometry to increase coverage and accuracy. Machine learning was used to integrate the mass spectrometry scores and assign probabilities to the protein-protein interactions. Among 4,087 different proteins identified with high confidence by mass spectrometry from 2,357 successful purifications, our core data set (median precision of 0.69) comprises 7,123 protein-protein interactions involving 2,708 proteins. A Markov clustering algorithm organized these interactions into 547 protein complexes averaging 4.9 subunits per complex, about half of them absent from the MIPS database, as well as 429 additional interactions between pairs of complexes. The data (all of which are available online) will help future studies on individual proteins as well as functional genomics and systems biology.     

DNA cloning in Streptomyces: resistance genes from antibiotic-producing species

The biochemical and morphological differentiation of actinomycetes makes them academically and economically interesting. Their secondary metabolites provide the majority of medically and agriculturally important antibiotics (streptomycete genes may also be the primary source of clinically important antibiotic resistance); their complex morphological developmental cycle involves a series of changes from vegetative mycelial growth to spore formation. Recombinant DNA technology would add a powerful new dimension to the analysis of these various aspects of actinomycete biology and would also facilitate the development of industrial strains with increased antibiotic yield, or capable of making new antibiotics. For most of these purposes, cloning of genes within and between actinomycetes is required to study the expression of particular genes in genetic backgrounds defined by mutations of the characters under study. To achieve this, we have now developed a method for molecular cloning involving the transfer of genes between unrelated streptomycetes.     

56K fibroblast protein not specific for Duchenne muscular dystrophy but for skin biopsy site

Recently, we reported the detection by two-dimensional gel electrophoresis of a 56,000 (56K)-molecular weight polypeptide that was present in cultured skin fibroblasts from normal males but was not detectable in fibroblasts from Duchenne muscular dystrophy (DMD) patients. Since then we have established that the 56K polypeptide is not present in skin fibroblasts from normal females, DMD carrier females, or in normal male fibroblasts obtained from sources other than the Repository for Mutant Human Cell Strains, Montreal. Further inquiry has led to the discovery that all the normal male fibroblast cultures obtained from the Montreal repository had been established from preputial skin. Fibroblast cultures from DMD patients, DMD carriers, as well as other normal individuals, had been derived from non-genital skin biopsies. Thus, the absence of the 56K polypeptide is not specific for DMD, but rather is related to the site of skin biopsy.     

The rate of incorporation of gaseous14CO2 into brain tissue constituents

Zusammenfassung Die¹⁴CO₂-Fixation verschiedener Fraktionen des Rattengehirnes wurde untersucht. Die Ratten wurden 15–120 min in gasförmigem¹⁴CO₂ exponiert und in flüssigem N₂ gefroren. Nach 15, 30, 60 und 120 min waren 9, 17, 21 und 35% vom Gesamt-¹⁴CO₂ in der Gehirnsubstanz organisch gebunden. Der grösste Teil des organischen¹⁴CO₂ fand sich in säurelöslicher Fraktion, während ein kleinerer Teil (etwa 10%) aus der Proteinfraktion isoliert werden konnte.     

Mammalian arylsulfatases A and B: relative rates of hydrolysis of artificial substrates

Rodent and bovine arylsulfatase B hydrolyze 4-methylumbelliferyl sulfate (4MUS) 10- to 30-fold more efficiently than arylsulfatase A. Therefore, 4MUS grossly underestimates arylsulfatase A activity in the presence of excess arylsulfatase B.