Probing DNA conformational changes with high temporal resolution by Tethered Particle Motion

The Tethered Particle Motion (TPM) technique informs about conformational changes of DNA molecules, e.g. upon looping or interaction with proteins, by tracking the Brownian motion of a particle probe tethered to a surface by a single DNA molecule and detecting changes of its amplitude of movement. We discuss in this context the time resolution of TPM, which strongly depends on the particle-DNA complex relaxation time, i.e. the characteristic time it takes to explore its configuration space by diffusion. By comparing theory, simulations and experiments, we propose a calibration of TPM at the dynamical level: we analyze how the relaxation time grows with both DNA contour length (from 401 to 2080 base pairs) and particle radius (from 20 to 150~nm). Notably we demonstrate that, for a particle of radius 20~nm or less, the hydrodynamic friction induced by the particle and the surface does not significantly slow down the DNA. This enables us to determine the optimal time resolution of TPM in distinct experimental contexts which can be as short as 20~ms.Comment: Improved version, to appear in Physical Biology. 10 pages + 10 pages of supporting materia

Control of Pre-mRNA Splicing by the General Splicing Factors PUF60 and U2AF65

Pre-mRNA splicing is a crucial step in gene expression, and accurate recognition of splice sites is an essential part of this process. Splice sites with weak matches to the consensus sequences are common, though it is not clear how such sites are efficiently utilized. Using an in vitro splicing-complementation approach, we identified PUF60 as a factor that promotes splicing of an intron with a weak 3' splice-site. PUF60 has homology to U2AF(65), a general splicing factor that facilitates 3' splice-site recognition at the early stages of spliceosome assembly. We demonstrate that PUF60 can functionally substitute for U2AF(65)in vitro, but splicing is strongly stimulated by the presence of both proteins. Reduction of either PUF60 or U2AF(65) in cells alters the splicing pattern of endogenous transcripts, consistent with the idea that regulation of PUF60 and U2AF(65) levels can dictate alternative splicing patterns. Our results indicate that recognition of 3' splice sites involves different U2AF-like molecules, and that modulation of these general splicing factors can have profound effects on splicing

Critical exponents at the ferromagnetic transition in tetrakis(diethylamino)ethylene-C60_{60} (TDAE-C60_{60})

Critical exponents at the ferromagnetic transition were measured for the first time in an organic ferromagnetic material tetrakis(dimethylamino)ethylene fullerene[60] (TDAE-C$_{60}$). From a complete magnetization-temperature-field data set near $T_{c}=16.1\pm 0.05,$ we determine the susceptibility and magnetization critical exponents $\gamma =1.22\pm 0.02$ and $\beta =0.75 \pm 0.03$ respectively, and the field vs. magnetization exponent at $T_{c}$ of $\delta =2.28\pm 0.14$. Hyperscaling is found to be violated by $\Omega \equiv d^{\prime}-d \approx -1/4$, suggesting that the onset of ferromagnetism can be related to percolation of a particular contact configuration of C$_{60}$ molecular orientations.Comment: 5 pages, including 3 figures; to appear in Phys. Rev. Let

Ferromagnetism and giant magnetoresistance in the rare earth fullerides Eu6-xSrxC60

We have studied crystal structure, magnetism and electric transport properties of a europium fulleride Eu6C60 and its Sr-substituted compounds, Eu6-xSrxC60. They have a bcc structure, which is an isostructure of other M6C60 (M represents an alkali atom or an alkaline earth atom). Magnetic measurements revealed that magnetic moment is ascribed to the divalent europium atom with S = 7/2 spin, and a ferromagnetic transition was observed at TC = 10 - 14 K. In Eu6C60, we also confirm the ferromagnetic transition by heat capacity measurement. The striking feature in Eu6-xSrxC60} is very large negative magnetoresistance at low temperature; the resistivity ratio \rho(H = 9 T)/\rho(H = 0 T) reaches almost 10^{-3} at 1 K in Eu6C60. Such large magnetoresistance is the manifestation of a strong pi-f interaction between conduction carriers on C60 and 4f electrons of Eu.Comment: 5 pages, 4 figure

Flavonoids in phylloclades discriminate endemic Semele androgyna chemotypes from Madeira

Thirty-five randomly-collected Semele androgyna Kunth samples were screened by RP-HPLC for their phenolic composition. Fraction analysis allowed the detection of 17 different compounds. According to their retention times and UV spectra obtained by diode array analysis, these phenolics represent three classes: phenolic acids, flavones and flavonols. Co-chromatography with specific standards enabled identification of quercetin, rutin and quercitrin in Semele tissues for the first time. Polymorphism based on phenolic composition was evaluated using multivariate analysis and showed four distinct S. androgyna clusters. This polymorphism was not associated with morphological diversity or different in ambient light intensities. Biochemical differentiation is thus present in this species. The application of multivariate analysis techniques to RP-HPLC data has allowed the classification of samples into two groups, previously proposed on the basis of morphological and cytotaxonomical information. Therefore, the use of phenolics as chemotaxonomic markers in Semele is highly recommended because of its diagnostic value, even at a subspecies level. Discriminant canonical analysis and Mahalanobis distances confirmed these clusters as recognisable chemosystematic units. However, these units do not support the separation of S. pterygophora.The Portuguese Foundation for Science and Technology (FCT) funded this work through the Centre of Macaronesian Studies (CEM). The authors are grateful to the Madeiran Centre of Science and Technology (CITMA), the Berardo Foundation and European Social Funding for financial assistance given during execution of this work. The assistance rendered by Mr Rogério Correia during field collection is gratefully acknowledged.info:eu-repo/semantics/publishedVersio

Gate-induced band ferromagnetism in an organic polymer

We propose that a chain of five-membered rings (polyaminotriazole) should be ferromagnetic with an appropriate doping that is envisaged to be feasible with an FET structure. The ferromagnetism is confirmed by a spin density functional calculation, which also shows that ferromagnetism survives the Peierls instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band ferromagnetism with the Hubbard model. This opens a new possibility of band ferromagnetism in purely organic polymers.Comment: 4 pages, 7 figure

Personality trait development in midlife: exploring the impact of psychological turning points

This study examined long-term personality trait development in midlife and explored the impact of psychological turning points on personality change. Selfdefined psychological turning points reflect major changes in the ways people think or feel about an important part of their life, such as work, family, and beliefs about themselves and about the world. This study used longitudinal data from the Midlife in the US survey to examine personality trait development in adults aged 40–60 years. The Big Five traits were assessed in 1995 and 2005 by means of self-descriptive adjectives. Seven types of self-identified psychological turning points were obtained in 1995. Results indicated relatively high stability with respect to rankorders and mean-levels of personality traits, and at the same time reliable individual differences in change. This implies that despite the relative stability of personality traits in the overall sample, some individuals show systematic deviations from the sample mean-levels. Psychological turning points in general showed very little influence on personality trait change, although some effects were found for specific types of turning points that warrant further research, such as discovering that a close friend or relative was a much better person than one thought they were

Inorganic carbon concentrating mechanisms in free-living and symbiotic dinoflagellates and chromerids

Photosynthetic dinoflagellates are ecologically and biogeochemically important in marine and freshwater environments. However, surprisingly little is known of how this group acquires inorganic carbon or how these diverse processes evolved. Consequently, how CO2 availability ultimately influences the success of dinoflagellates over space and time remains poorly resolved compared to other microalgal groups. Here we review the evidence. Photosynthetic core dinoflagellates have a Form II RuBisCO (replaced by Form IB or Form ID in derived dinoflagellates). The in vitro kinetics of the Form II RuBisCO from dinoflagellates are largely unknown, but dinoflagellates with Form II (and other) RuBisCOs have inorganic carbon concentrating mechanisms (CCMs), as indicated by in vivo internal inorganic C accumulation and affinity for external inorganic C. However, the location of the membrane(s) at which the essential active transport component(s) of the CCM occur(s) is (are) unresolved; isolation and characterization of functionally competent chloroplasts would help in this respect. Endosymbiotic Symbiodiniaceae (in Foraminifera, Acantharia, Radiolaria, Ciliata, Porifera, Acoela, Cnidaria, and Mollusca) obtain inorganic C by transport from seawater through host tissue. In corals this transport apparently provides an inorganic C concentration around the photobiont that obviates the need for photobiont CCM. This is not the case for tridacnid bivalves, medusae, or, possibly, Foraminifera. Overcoming these long-standing knowledge gaps relies on technical advances (e.g., the in vitro kinetics of Form II RuBisCO) that can functionally track the fate of inorganic C forms