DNA topoisomerase II completely removes DNA intertwining, or catenation, between sister chromatids before they are segregated during cell division. How this occurs throughout the genome is poorly understood. We demonstrate that in yeast, centromeric plasmids undergo a dramatic change in their topology as the cells pass through mitosis. This change is characterized by positive supercoiling of the DNA and requires mitotic spindles and the condensin factor Smc2. When mitotic positive supercoiling occurs on decatenated DNA, it is rapidly relaxed by topoisomerase II. However, when positive supercoiling takes place in catenated plasmid, topoisomerase II activity is directed toward decatenation of the molecules before relaxation. Thus, a topological change on DNA drives topoisomerase II to decatenate molecules during mitosis, potentially driving the full decatenation of the genome.

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Background: Changes in DNA topology during replication are still poorly understood. Results: Classical genetics and two-dimensional agarose gel electrophoresis showed that RIs tensioned in the absence of Topo IV. Conclusion:The results indicated that replication forks swivel in vivo leading to the formation of precatenanes as replication progresses. Significance: This conclusion ends a long lasting debate on the formation of precatenanes during replication.

We systematically varied conditions of two-dimensional (2D) agarose gel electrophoresis to optimize separation of DNA topoisomers that differ either by the extent of knotting, the extent of catenation or the extent of supercoiling. To this aim we compared electrophoretic behavior of three different families of DNA topoisomers: (i) supercoiled DNA molecules, where supercoiling covered the range extending from covalently closed relaxed up to naturally supercoiled DNA molecules; (ii) postreplicative catenanes with catenation number increasing from 1 to ∼15, where both catenated rings were nicked; (iii) knotted but nicked DNA molecules with a naturally arising spectrum of knots. For better comparison, we studied topoisomer families where each member had the same total molecular mass. For knotted and supercoiled molecules, we analyzed dimeric plasmids whereas catenanes were composed of monomeric forms of the same plasmid. We observed that catenated, knotted and supercoiled families of topoisomers showed different reactions to changes of agarose concentration and voltage during electrophoresis. These differences permitted us to optimize conditions for their separation and shed light on physical characteristics of these different types of DNA topoisomers during electrophoresis.

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Introduction. Mexico harbors a great diversity of Spondias purpurea ecotypes, whose fruit is called Mexican plum and has a good consumer acceptance because of its organoleptic and nutritional characteristics. Materials and methods. The concentrations of metabolites in 11 ecotypes of Mexican plum were determined from samples of rind (epicarp) and pulp originating from fresh seasonal fruit. Results and discussion. The mass of these fruits varied from 11.1 to 35.0 g, and the epicarp color ranged from purple and red, to orange and yellow. The content of total soluble solids, total sugars, and vitamin C was of 9.4−18.2 • Brix, 101.0−185.9 mg g −1 fresh weight (FW), and 0.6−2.1 mg g −1 FW, respectively. The total phenolic content was always higher in the epicarp (3.7 mg g −1 FW) than in the pulp (1.3 mg −1 FW), as was the total content of carotenoids and the levels of antioxidant activity. Additionally, positive correlations could be established between antioxidant activity and total phenolics, total phenolics and total carotenoids, and between the antioxidant activity in the epicarp and the total content of vitamin C. In addition, negative correlations were found between hue and the carotenoid content of the pulp, and between hue and the antioxidant activity in the epicarp and pulp. Conclusion. The results suggest that a higher content of phenols, carotenoids, and vitamin C, together with a purple or red coloration of the epicarp, can all be associated with an increase in the antioxidant activities of the epicarp and pulp of the Mexican plum.Keywords: Mexico / Latin America / Mexican plum / Spondias purpurea / antioxidant activity / carotenoids / phenolics / vitamin C / nutritional value Résumé -Attributs de qualité et composés fonctionnels des fruits de divers écotypes de prune mexicaine (Spondias purpurea L.). Introduction. Le Mexique abrite une grande diversité d'écotypes de Spondias purpurea dont le fruit est appelé prune mexicaine et possède une bonne image auprès des consommateurs en raison de ses caractéristiques organoleptiques et nutritionnelles. Matériel et méthodes. Les concentrations en métabolites de 11 écotypes de prune mexicaine ont été déterminées à partir d'échantillons de la peau (épicarpe) et de la pulpe de fruits frais de saison. Résultats et discussion. La masse de ces fruits s'est inscrite entre 11,1 et 35,0 g, et la couleur de l'épicarpe pouvait varier du rouge violacé à l'orange et au jaune. Le contenu en solides solubles totaux, en sucres totaux, et en vitamine C variait de 9,4 à 18,2 • Brix, de 101,0 à 185,9 mg g −1 poids frais (FW), et de 0,6 à 2,1 mg g −1 FW, respectivement. Le contenu phénolique était toujours plus élevé dans l'épicarpe (3,7 mg g −1 FW) que dans la pulpe (1,3 mg g −1 FW), tout comme la teneur en caroténoïdes totaux et les niveaux d'activité anti-oxydante. En outre, des corrélations positives ont pu être établies entre l'activité anti-oxydante et les composés phénoliques totaux, entre les composés phénoliques totaux et les caroténoïdes totaux, et entre l'activité anti-oxyda...

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