1,720,956 research outputs found
Phosphoenolpyruvate is a signal metabolite in transcriptional control of the cbb CO2 fixation operons in Ralstonia eutropha
No full textThe two highly homologous cbb operons of the facultative chemoautotroph Ralstonia eutropha H16 encode most enzymes of the Calvin-Benson-Bassham carbon reduction cycle. Their transcriptional regulation was investigated both in vitro and in vivo to identify a metabolic signal involved in this process. For this purpose an in vitro transcription system employing the DNA-dependent RNA polymerase purified from R. eutropha was established. The enzyme from Escherichia coli was also used in verifying comparative studies. Plasmid DNA carrying the control region of the chromosomal cbb operon served as template. In the homologous as well as the heterologous system specific transcripts synthesized under the control of the operon promoter P-cbbL were observed, depending on the structure of the tested promoter variant as well as the presence or absence of the activator protein CbbR. Unlike mutationally improved PcbbL variants, the wild-type promoter remained inactive, even in the presence of CbbR together with various potential signal metabolites. CbbR stimulated PcbbL mutants with intermediate basal activity. Phosphoenolpyruvate (PEP) was identified as a negative effector of CbbR that inhibited P-cbbL-directed transcription and increased the operator-binding affinity of the protein. This CbbR-mediated inhibition was confirmed by assaying wild-type PcbbL operon fusions in glucose- or succinate-grown cells of E. coli, which contain greatly different concentrations of PEP. It is concluded that at least one additional protein must participate in the overall control of the cbb operons in R. eutropha
Phosphoenolpyruvate is a signal metabolite in transcriptional control of the cbb CO2 fixation operons in Ralstonia eutropha
No full textThe two highly homologous cbb operons of the facultative chemoautotroph Ralstonia eutropha H16 encode most enzymes of the Calvin-Benson-Bassham carbon reduction cycle. Their transcriptional regulation was investigated both in vitro and in vivo to identify a metabolic signal involved in this process. For this purpose an in vitro transcription system employing the DNA-dependent RNA polymerase purified from R. eutropha was established. The enzyme from Escherichia coli was also used in verifying comparative studies. Plasmid DNA carrying the control region of the chromosomal cbb operon served as template. In the homologous as well as the heterologous system specific transcripts synthesized under the control of the operon promoter P-cbbL were observed, depending on the structure of the tested promoter variant as well as the presence or absence of the activator protein CbbR. Unlike mutationally improved PcbbL variants, the wild-type promoter remained inactive, even in the presence of CbbR together with various potential signal metabolites. CbbR stimulated PcbbL mutants with intermediate basal activity. Phosphoenolpyruvate (PEP) was identified as a negative effector of CbbR that inhibited P-cbbL-directed transcription and increased the operator-binding affinity of the protein. This CbbR-mediated inhibition was confirmed by assaying wild-type PcbbL operon fusions in glucose- or succinate-grown cells of E. coli, which contain greatly different concentrations of PEP. It is concluded that at least one additional protein must participate in the overall control of the cbb operons in R. eutropha
Differential effect of acute and permanent heat shock protein 70 overexpression in tumor cells on lysability by cytotoxic T lymphocytes
No full textWe have shown previously that acute heat shock protein (Hsp) 70 induction in a human melanoma cell line containing a doxycycline-inducible Hsp70 expression construct increases lysability of these tumor cells by cytotoxic T lymphocyte (CTL) without interfering with MHC class I expression and antigen presentation. The same parental melanoma cell line has now been transduced retrovirally to overexpress Hsp70 permanently. Here we demonstrate that MHC class I cell surface expression is again not altered and that these cells, in contrast with acutely Hsp70 overexpressing cells, do not show augmentation of CTL-mediated apoptosis. Also, long-term induction of Hsp70 in cells with the doxycycline-inducible Hsp70 construct leads to abrogation of increased lysability. Because, furthermore, after heat shock the same permanently Hsp70 overexpressing cells show Hsp70 induction and increased lysability, it is hypothesized that acutely available Hsp70 is able to chaperone proteins that are involved in CTL-mediated apoptosis of target cells and to thereby improve their lysability. We also observed that permanent but not acute Hsp70 overexpression resulted in decreased levels of Hsc70, the constitutively expressed member of the Hsp70 family. Down-regulation of Hsc70 occurs at the post-transcriptional level and can be observed also after long-term induction of Hsp70 in cells containing the doxycycline-inducible expression system. Hsc70 down-regulation might reflect a functional integration of the overexpressed Hsp70 on the basis of a chaperone network so that only acute induction will provide Hsp70 that can improve tumor cell lysability. The implications of the differential effect of acute versus permanent Hsp70 overexpression for tumor therapy are discussed
Differential effect of acute and permanent heat shock protein 70 overexpression in tumor cells on lysability by cytotoxic T lymphocytes
No full textWe have shown previously that acute heat shock protein (Hsp) 70 induction in a human melanoma cell line containing a doxycycline-inducible Hsp70 expression construct increases lysability of these tumor cells by cytotoxic T lymphocyte (CTL) without interfering with MHC class I expression and antigen presentation. The same parental melanoma cell line has now been transduced retrovirally to overexpress Hsp70 permanently. Here we demonstrate that MHC class I cell surface expression is again not altered and that these cells, in contrast with acutely Hsp70 overexpressing cells, do not show augmentation of CTL-mediated apoptosis. Also, long-term induction of Hsp70 in cells with the doxycycline-inducible Hsp70 construct leads to abrogation of increased lysability. Because, furthermore, after heat shock the same permanently Hsp70 overexpressing cells show Hsp70 induction and increased lysability, it is hypothesized that acutely available Hsp70 is able to chaperone proteins that are involved in CTL-mediated apoptosis of target cells and to thereby improve their lysability. We also observed that permanent but not acute Hsp70 overexpression resulted in decreased levels of Hsc70, the constitutively expressed member of the Hsp70 family. Down-regulation of Hsc70 occurs at the post-transcriptional level and can be observed also after long-term induction of Hsp70 in cells containing the doxycycline-inducible expression system. Hsc70 down-regulation might reflect a functional integration of the overexpressed Hsp70 on the basis of a chaperone network so that only acute induction will provide Hsp70 that can improve tumor cell lysability. The implications of the differential effect of acute versus permanent Hsp70 overexpression for tumor therapy 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
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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