Brownian dynamics simulation of DNA condensation.

DNA condensation observed in vitro with the addition of polyvalent counterions is due to intermolecular attractive forces. We introduce a quantitative model of these forces in a Brownian dynamics simulation in addition to a standard mean-field Poisson-Boltzmann repulsion. The comparison of a theoretical value of the effective diameter calculated from the second virial coefficient in cylindrical geometry with some experimental results allows a quantitative evaluation of the one-parameter attractive potential. We show afterward that with a sufficient concentration of divalent salt (typically approximately 20 mM MgCl(2)), supercoiled DNA adopts a collapsed form where opposing segments of interwound regions present zones of lateral contact. However, under the same conditions the same plasmid without torsional stress does not collapse. The condensed molecules present coexisting open and collapsed plectonemic regions. Furthermore, simulations show that circular DNA in 50% methanol solutions with 20 mM MgCl(2) aggregates without the requirement of torsional energy. This confirms known experimental results. Finally, a simulated DNA molecule confined in a box of variable size also presents some local collapsed zones in 20 mM MgCl(2) above a critical concentration of the DNA. Conformational entropy reduction obtained either by supercoiling or by confinement seems thus to play a crucial role in all forms of condensation of DNA.

Monsieur Badin : scène de la vie de bureau, saynète en 1 acte (Paris, Grand-Guignol, 13 avril 1897) ; et l'Extra-Lucide : saynète en 1 acte (Paris, Carillon, 17 mai 1897) / Georges Courteline

Collection : Les pièces à succès ; N° 18

Les français en Italie : histoire des interventions françaises en Italie depuis Pépin le Bref, jusqu'à nos jours, 721-1849 / par Robert Hyenne

Collection : Bibliothèque pour tous illustrée

Les cent nouvelles nouvelles. Tome 1 / publ. d'après le seul ms. connu avec introd. et notes par M. Thomas Wright

[Cent nouvelles nouvelles (français moyen). 1857-1858]

Les cent nouvelles nouvelles. Tome 2 / publ. d'après le seul ms. connu avec introd. et notes par M. Thomas Wright

[Cent nouvelles nouvelles (français moyen). 1857-1858]

Oesophagite à éosinophiles [Eosinophilic esophagitis].

Eosinophilic esophagitis is a recent diagnosis, of growing interest and prevalence. It has to be considered by every physician when facing any adult or pediatric case of dysphagia, food impaction, and symptoms of GERD (gastroesophageal reflux disease) resistant to proton-pump inhibitor treatment. The diagnosis is made by combining clinical symptoms and endoscopic signs, supported by biopsies of the mucosa, which should show more than 15 eosinophils per high power field. The etiology seems to be of allergic origin, and a full immuno-allergic testing should be made. Recommendations for the treatment are to calm down the inflammatory process by proton-pump inhibitors, and to give topical steroids, keeping the systemic treatment for acute severe cases. In cases of esophageal stenoses, dilations can be undertaken, but with a high risk of recurrence.