1,721,004 research outputs found
The interaction between initiation factor 3 and 30 S ribosomal subunits studied by high-resolution 1H NMR spectroscopy
No full textThe interaction between Escherichia coli translational initiation factor 3 (IF-3) (Mr = 20668) and 30 S ribosomal subunits or fragmented 16 S rRNA was followed by 1H NMR spectroscopy. Upon addition of increasing yet largely substoichiometric amounts of deuterated 30 S ribosomal subunits, selective line broadenings and some chemical shift changes were observed. These effects can be fully reversed by increasing the temperature and/or the ionic strength. The selective line broadenings, which are explained by a medium-fast to fast exchange dynamics between free and bound IF-3 with loss of internal mobility of the protons, shed light on the amino acid residues of IF-3 involved in or affected by the binding to the 30 S subunits. Some effects (i.e. implication of 1 tyrosine, 1 phenylalanine, and some arginine and lysine residues) are seen with both 30 S subunits and rRNA while others (i.e. implication of a second tyrosine or phenylalanine residue of a group of hydrophobic residues and, possibly, of the single histidine residue), seen only or preferentially with 30 S subunits, may reflect additional interactions exclusively occurring at the ribosomal level
Structure-function relationship in Escherichia coli initiation factors. Environment of the Cys residue and evidence for a hydrophobic region in initiation factor IF3 by fluorescence and ESR spectroscopy
No full textTranslation of mRNA with degenerate initiation triplet AUU displays high IF2 dependence and is subject to IF3 repression
No full textStructure-function relationship in Escherichia coli translational initiation factors. Characterization of IF-3 by high resolution 1H NMR spectroscopy
No full textTranslational initiation factor-3 (IF-3) was characterized by 1H NMR spectroscopy as a function of pH and temperature and following chemical modifications. Spin-lattice relaxation times for individual resonances and bands were also measured. Several resonances were assigned to different amino acid residues by different criteria. Among these are the CH3-N of the N-terminal methionine which appears free, mobile, and very sensitive to the modification of several physicochemical parameters as well as the 3,5 and 2,6 protons of the three tyrosines (two of which play a role in the function of IF-3) which were found to be located in different magnetic environments. Two of these residues appear to be close to each other and in the vicinity of a slow reacting arginine within the tertiary structure of the factor. The properties and the titration behavior of the imidazole proton resonances suggest that the single His residue is partially buried in the protein structure. Characteristic of the IF-3 spectrum also is the presence of an abundant subset of Arg delta-CH2, Lys epsilon-CH2, and CH3 protons displaying clear cut upfield perturbations. These are probably due to the coming together of two or more apolar "fronts" which possibly arise from distant parts of the molecule and result in the close proximity between aromatic rings and aliphatic side chains. The IF-3 spectrum also includes several distinct methyl resonances significantly shifted upfield by aromatic ring currents. Overall, the characteristics of the spectrum, its relative insensitivity to temperature and ionic strength, and the existence of extensive cross-relaxation phenomena indicate that IF-3 has a highly folded tertiary structure with abundant hydrophobic regions. In spite of some heterogeneity in the distribution of the side chain environments, no indication was found for the existence of distinct domains or, at least, of extensive regions with higher mobility
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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