1,721,218 research outputs found
Caratterizzazione strutturale e funzionale della topoisomerasi IB umana e dei suoi mutanti
Full text linkLa DNA topoisomerasi IB umana è un enzima monomerico essenziale nel risolvere problemi topologici generati durante procesi chiave nucleari quali la replicazione, trascrizione, combinazione e riparazione del DNA. Latopo IB rilassa DNA superavvolti sia negativi che positivi in assenza di cationi metallici, attraverso la rottura transiente di un singolo filamento di DNA. Durante il ciclo catalitico il residuo Tyr723 viene usato come nucleofilo per rompere il legame fosfodiesterico del backbone del DNA generando un complesso covalente enzima-DNA all'estremità 3' del filamento tagliato. Il gruppo ossidrile 5' del filamento tagliato è libero di ruotare e di agire come nucleofilo attaccando il gruppo fosfato per rompere il legame tra il DNA e l'enzima risaldando il filamento precedentemente tagliato. Secondo studi cristallografici e di proteolisi limitata la topo IB è organizzata in quattro domini: N-terminale, core, linker e C-terminale che contiene il residuo attivo della Tyr723. L'enzima inoltre risulta essere l'unico bersaglio di farmaci chemioterapici quali la camptotecina ed i suoi derivati. Studi di mutanti ipersensibili, come la topoisomerasi I Asp677Gly-Val703Ile, permettono di comprendere i meccanismi alla base del funzionamento dell'enzima e della sua interazione con la droga ed intercorrelazione tra i diversi domini proteici. A tal fine sono stati eseguiti saggi di caratterizzazione biochimica del mutante in vivo ed in vitro analizzando le principali fasi del ciclo. Lo sviluppo sempre maggiore di nuovo farmaci antitumorali ci ha portato a volgere l'attenzione sull'effetto inibitorio del cEPA e a comprenderne il meccanismo. Gli esperimenti mostrano che il cEPA ha un meccanismo differrente dalla CPT inibendo il taglio dell'enzima sul DNA substrato sebbene permetta la formazione del complesso non covalente enzima-DNA. Di particolare interesse è il dominio N-terminale, in quanto è l'unica regione dell'enzima con una struttura 3D sconosciuta, in quanto non è possibile cristallizzarla. Il dominio è stato overespresso in E. coli BL21 come proteina di fusione con la GST. Sono stati esegiuti studi preliminari di struttura mediante tecniche spettroscopiche di fluorescenza, di dicroismo circolare e di NMR monodimensionale. Questi spettri indicano un eqiuilibrio tra regioni strutturate e non strutturate, ma per ricevere ulteriori informazioni strutturali è necessario eseguire spettri NMR bidimensionali producendo il dominio marcato con isotopi N15 e C13.Human DNA topoisomerase IB (topo IN) is an essential monomeric enzyme involved in resolving the torsional stress assiciated with DNA replication, trascription and chromatin condensation. Topo IB catalyzes changes in the supehelical state of the duplex DNA by transiently breaking a single strand allowing the broken strand to move through the break. Phosphodiester bond energy is preserved during catalysis through the formation of a transient phosphotyrosine bond between the active-site tyrosine and the 3' end of the broken strand. According to X-ray crystallography and biochemical analysyses topo IB is organized into four domains: N-terminal domain,core, linker and C-terminal domain which contains the active site Tyr723. The topo IB is also an important target of the antitumor drug camptothecin for chemotherapy of uman cancers. The biochemical and structural-dynamical properties of the Asp677Gly-Val703Ile double mutant displaying a pronounced CPT sensitivity as been investigated to better understad the action mechanism of the enzyme and the interaction of CPT with the cleavable topoI-DNA complex. The results have shown that the CPT hypersensitivity of the mutations its done to a reduction of its religation rate and demonstrated the occurrence of a long range communication between domains localized far away one from the other.The inhibition efficiency on human topo IB wild type of the cEPA has been investigated analyzing the different steps of the enzyme catalytic cycle. The experiments show that cEPA has a mechanism different from CPT, inhibiting the cleavage of the enzyme on the DNA although permitting the non covalent enzyme-DNA interaction. The human topoI N-terminal domain is the only region of the enzyme with an unknown 3D structure since it is not possible to crystallize it. This domain has been overproduced into E.coli BL21,to carry out preliminary spectroscopic analysis consisting of CD, fluorescence and NMR spectra. The spectra indicate an equilibrium between the structured and unstructured regions. We are now producing the isotope labeled protein,growing the bacterial cells in minimum medium containing N15,in the attempt to gain further structural information by high-field 2D NMR spectroscopy
A method to reveal supply chains in order to set up effective and sustainable city logistics solutions
No full textA current key challenge in the field of urban freight transport is creating value and business opportunities through city logistics. This requires an extensive knowledge of the composition of urban economic structure, organization and management of supply chains, and actors’ sensitivity to market signals. Within this context, the paper reports the findings of the LOGeco – LOGistica ecologica project. Within LOGeco, the authors developed a method to collect and analyze data in order to set up city logistics solutions based on existing supply chains, public-private cooperation and Business Opportunity Plans for the private sector. The method has been validated in a pedestrian area of the historic centre of Rome, the Renaissance district named «Tridente». The method consists of a survey technique which involves the following steps: a census of activities representing the sources of demand for urban freight transport and their characterization; sampling; web-based survey; database collection, analysis
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
Revealing urban goods movements: empirical evidences from some European cities
Full text linkThe paper compares the characteristics of urban freight transport in some European cities, implementing a methodology which uses similar interviews with retailers and transport operators. The main objective of this study is to evaluate the similarities and differences in terms of socio-economic characteristics and commercial structures, and current distribution patterns followed by different transport and logistics operators. The study shows the flexibility of the methodology used in different applicative contexts and points out that there are some different patterns of urban distribution that need to be taken into account when implementing city logistics measures
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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