1,720,972 research outputs found
A single-molecule approach to understanding sister chromatid cohesion establishment
No full textSister chromatid cohesion is established by the cohesin complex during DNA replication in S phase. This process requires cohesin to transition from binding to one DNA strand to co-entrapping the two newly synthesised sister chromatids. Passage of the eukaryotic replisome through the ring-shaped cohesin complex has been proposed as a fail-safe mechanism to ensure that cohesin entraps the two sister chromatids, enabling their faithful segregation during cell division. However, whether replisomes can indeed pass through cohesin remains unknown, and the details of replisome-cohesin encounters are poorly understood.
Here, I use single molecule fluorescence microscopy to directly visualise encounters between biochemically reconstituted DNA replication forks and cohesin complexes. On a linear forked DNA, I find that the translocating replicative CMG helicase acts as an obstacle to cohesin. The obstacle is overcome by cohesin at low frequencies, which increase in presence of added replisome components with known sister chromatid cohesion establishment functions. When lateral cohesin diffusion is prevented, CMG passage, during which cohesin retains topological DNA entrapment, becomes the predominant outcome. Finally, I find that the likelihood of passage also increases when an active replisome encounters cohesin, resulting in successful cohesion establishment between the two replication products. Interestingly, when cohesin’s ability to diffuse on DNA is blocked, replication fork passage is efficiently achieved independently of cohesion establishment factors.
My findings resolve a long-held puzzle by visualising live sister chromatid cohesion establishment as the replisome passes the cohesin ring, providing new insights into the molecular mechanisms of sister chromatid cohesion establishment.Open Acces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Multiple DNA repair pathways contribute to cell lethality in checkpoint mutants
No full textTrabajo presentado al Midterm Review Meeting; Checkpoints, DNA Damage Response and Cancer, celebrado en Milán el 3 de noviembre de 2005.The checkpoint kinases Mec1 and Rad53 play an essential role in stabilizing stalled
DNA replication forks. We have initiated a genetic screen to identify mutants that
render checkpoint-defective yeast cells more resistant to fork-stalling agents (e.g.
hydroxyurea, MMS, etc). We have screened the entire library for mutants with
heightened resistance to hydroxyurea when the checkpoint has been compromised with
caffeine. From this, we have identified mutants in several repair pathways, and
therefore, we decided to check for caffeine plus hydroxyurea resistance in several
members of the main repair pathways. Our conclusions indicate that different repair
pathways contribute to lethality in checkpoint mutants.
We have also found that there is a significant Increase in HU-resistance when
combining different repair mutants in rad53-null background. However, none of these
multiple mutants is able to rescue viability completely, indicating that there are other
requirements to maintain fork stability in the absence of rad53.Peer reviewe
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Different repair pathways are involved in checkpoint-dependent replication fork stabilization
No full textTrabajo presentado al Mini-Symposium RTN: Genome Integrity, celebrado en Paris del 11 al 12 de diciembre de 2006.The ability to survive spontaneous and induced DNA damage depends on S phase checkpoints, which act by inhibiting late origin firing, stabilizing replication forks and preventing S phase progression. It has been previously shown in our lab that the preservation of fork integrity, rather than inhibition of origin firing, is essential to mantain cell viability under DNA damage conditions. Therefore, we are interested in the identification of checkpoint-dependent pathways involved in stabilization of the forks. We have initiated a genetic screen to identify mutants that render checkpoint-defective yeast cells more resistant to fork-stalling agents. In our first attempt we identified a number of mutants but we were unable to complement the mutants because of the partially penetrant phenotype. We have screened the entire deletion library for mutants with heightened resistance to hydroxyurea when the checkpoint has been compromised with caffeine. From this, we have identified mutants in several repair pathways, and therefore, we decided to check for caffeine plus hydroxyurea resistance in several members of the main repair pathways. Our conclusions indicate that different repair pathways contribute to lethality in checkpoint mutants.Peer Reviewe
Unchecked nick ligation can promote localized genome re-replication
No full textSingle-stranded DNA breaks, or nicks, are amongst the most common forms of DNA damage in cells. They can be repaired by ligation; however, if a nick occurs just ahead of an approaching replisome, the outcome is a collapsed replication fork comprising a single-ended double-strand break and a 'hybrid nick' with parental DNA on one side and nascent DNA on the other (Figure 1A). We realized that in eukaryotic cells, where replication initiates from multiple replication origins, a fork from an adjacent origin can promote localized re-replication if the hybrid nick is ligated. We have modelled this situation with purified proteins in vitro and have found that there is, indeed, an additional hazard that eukaryotic replisomes face. We discuss how this problem might be mitigated
- …
