1,721,130 research outputs found
Regulation of maize Ac/Ds transposition by replication and DNA methylation
Full text linkIn maize the transposable elements Activator/Dissociation (Ac/Ds) transpose shortly after
replication from one of the two resulting chromatids ("chromatid selectivity"). A model
was suggested that explains this phenomenon as a consequence of different Ac transposase
binding to holo-, hemi- and unmethylated transposon ends (Wang et al., 1996). It assumes
that before replication the element is holomethylated and does not transpose because TPase
can not bind to the transposon ends. Shortly after replication one of the two differentially
hemimethylated daughter transposons should become transposition competent.
However, DNA methylation-mediated replication dependence does not completely explain
the behavior of Ac/Ds transposition. In several studies performed in monocot hosts, it was
found that in a transient assay Ac/Ds element excision from extrachromosomal geminivirus
vectors occurs only during vector replication, although the transfected DNAs were not Cmethylated.
In this work the correlation between Ds transposition, DNA replication and DNA
methylation in the dicot species Petunia hybrida was studied. Ds reporter vectors
harboring TYLCV (Tomato Yellow Leaf Curl Virus) geminivirus replicon sequences and
replicating in transfected petunia cells were constructed. It has been shown that the
transposition of a Ds element from an extrachromosomal vector in petunia cells is
regulated by DNA replication in a methylation-dependent and -independent mode.
Holomethylation completely inhibits Ds excision from a non-replicating plasmid, whereas
Ds transposition is restored by replication. Moreover, Ds elements that are hemimethylated
on one DNA strand transpose in the absence of replication, whereas methylation on the
complementary DNA strand results in at least 6.3-fold reduced excision frequencies. These
data strongly support the transposition model of Wang et al. (1996).
Beyond that, Ds transposition is strongly promoted by replication also in the absence of
methylation. It has been shown that in petunia cells, unlike monocot hosts, replication is
not a prerequisite for Ds transposition, nevertheless it enhances Ds transposition by at least
a factor of 7.5. Moreover, replication promotes the formation of a predominant excision
footprint. Implications on the mechanism and regulation of Ac/Ds transposition are
discussed
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
Light-harvesting chlorophyll a/b proteins (LHCII) populations in phosphorylated membranes
No full textVariations 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
Heat dissipation in the moss Physcomitrella patens: evolution of protection mechanisms upon land colonization
No full textInvited Lectur
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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