Single-molecule observation of the induction of k-turn RNA structure on binding L7Ae protein

AbstractThe k-turn is a commonly occurring structural motif that introduces a tight kink into duplex RNA. In free solution, it can exist in an extended form, or by folding into the kinked structure. Binding of proteins including the L7Ae family can induce the formation of the kinked geometry, raising the question of whether this occurs by passive selection of the kinked structure, or a more active process in which the protein manipulates the RNA structure. We have devised a single-molecule experiment whereby immobilized L7Ae protein binds Cy3-Cy5-labeled RNA from free solution. We find that all bound RNA is in the kinked geometry, with no evidence for transitions to an extended form at the millisecond timescale of the camera. Furthermore, real-time binding experiments provide no evidence for a more extended intermediate even at the earliest times, at a time resolution of 16 ms. The data support a passive conformational selection model by which the protein selects a fraction of RNA that is already in the kinked conformation, thereby drawing the equilibrium into this form

Surveying And Mathematics Education In Early America

The history of mathematics education during colonial America and early republic is an underprivileged subject. This thesis focuses on one aspect of this broad topic, the interdependence of land surveying and mathematical instruction. By analyzing the mathematical content of surveying manuals and by locating relevant newspaper advertisements, I conclude that the interdependence not only benefited the American mathematics education at its beginnings, but was instrumental in starting it

Interpreting Mathematics: Some Educational Considerations

This work contains several contributions supporting the idea that everyone can use mathematics to mold a personal niche in the social milieu by interpreting mathematical notions and results in one's own way. I include an autobiographical piece about my mathematical experience; a literature review of authors who influenced my thinking; a description of a seminar I designed to teach and test my views on interpreting mathematics; some applications to mathematical topics; and a list of references. Interpreting mathematics reflects the personal perspective of each individual on a particular piece of mathematics, on mathematics as a whole, or on everything mathematical in between; it has nothing to do with truth-it can be as plausible as the mathematics it concerns but it can also be fiction, eventually. The ability to interpret mathematics is different from the learning of mathematics per se-and it is a gateway to entrepreneurial uses of mathematics

The best writing on mathematics 2014

This annual anthology brings together the year's finest mathematics writing from around the world. Featuring promising new voices alongside some of the foremost names in the field, The Best Writing on Mathematics 2014 makes available to a wide audience many articles not easily found anywhere else-and you don't need to be a mathematician to enjoy them. These writings offer surprising insights into the nature, meaning, and practice of mathematics today. They delve into the history, philosophy, teaching, and everyday occurrences of math, and take readers behind the scenes of today's hottest mat

Structural Preference for Changes in the Direction of the Ca(2+)-Induced Transition: A Study of the Regulatory Domain of Skeletal Troponin-C

The determinants for specificity in the Ca(2+)-dependent response of the regulatory N-terminal domain of skeletal troponin-C are a combination of intrinsic and induced properties. We characterized computationally the intrinsic propensity of this domain for structural changes similar to those observed experimentally in the Ca(2+)-induced transition. The preference for such changes was assessed by comparing the structural effect of the harmonic and quasiharmonic vibrations specific for each Ca(2+) occupancy with crystallographic data. Results show that only the Ca(2+)-saturated form of the protein features a slow vibrational motion preparatory for the transition. From the characteristics of this mode, we identified a molecular mechanism for transition, by which residues 42-51 of helix B and of the adjacent linker move toward helices (A, D), and bind to the surface used by the protein to interact with troponin-I. By obstructing the access of the target to hydrophobic residues important in the formation of the complex, helix B and the adjacent linker act as an autoinhibitory structural element. Specific properties of the methionines at the interaction surface were found to favor the binding of the autoinhibitory region. Located over hydrophobic residues critical for binding, the methionines are easily displaceable to increase the accessibility of these residues to molecular encounter

La pratique du

La plus grande partie du travail d’accompagnement des sujets sans domicile fixe consiste à créer un lien suffisamment solide, durable, et à réamorcer quelques pans de la « socialité » interne. En effet, la dynamique relationnelle de ces sujets SDF s’est désorganisée en réaction à un vide central dans la personnalité résultant des failles du lien primaire, elles-mêmes réactualisées par la violence de la scène sociale. Le lien d’accompagnement doit alors prendre garde à ne pas exercer une violence supplémentaire. Les auteurs proposent de mettre en lumière un certain nombre de processus à l’œuvre dans la démarche dite de « l’aller-vers » auprès de ces sujets sans demande. La perspective clinique appliquée à l’aller-vers permet de saisir des opportunités interactionnelles, de relancer les processus de liaison, et, éventuellement, de poser les jalons nécessaires pour d’autres soins. Cette démarche passe en grande partie par un « accordage affectif mutuel », mais aussi par un « bricolage » continu du cadre, qui n’est pas sans lien ni sans effet sur l’organisation psychodynamique de ces sujets. D’autre part, ce « bricolage » du cadre implique une tension dans la position soignante qu’il convient d’éclairer. Les auteurs proposent ainsi de considérer la démarche « d’aller-vers » à la lumière du Squiggle Game proposé par Winnicott, c’est-à-dire comme un temps d’interaction et d’accordage fait de transactions ici infra-verbales et sensorielles