par Bourguignon, Marie-France 
;Bourgaux, Pierre
Référence Biochimica et biophysica acta, N. Nucleic acids and protein synthesis, 169, 2, page (476-487)
Publication Publié, 1968-12
;Bourgaux, Pierre Référence Biochimica et biophysica acta, N. Nucleic acids and protein synthesis, 169, 2, page (476-487)
Publication Publié, 1968-12
Article révisé par les pairs
| Résumé : | 1. 1. The covalently-closed circular form (component I) from polyoma virus DNA either untreated or heated at various temperatures in 10 % formaldehyde was spread by the Kleinschmidt method and examined under the electron microscope. Untreated preparations were found to consist essentially of tightly supercoiled molecules. 2. 2. Heating the preparations in the presence of formaldehyde first untwisted the molecules. Beyond the equivalence temperature (40°), however, molecules with superhelical turns were again evident, together with untwisted or poorly twisted circular molecules. 3. 3. Spreading the DNA at 37° instead of 22° markedly reduced the number of twists of native molecules. Under these conditions, a special shadowing procedure showed the supercoiling to be generally right-handed, while it was predominantly left-handed in largely denatured molecules. Unexpected handedness was observed in a low but significant number of cases. In view of these data, the origin of supercoiling was studied. © 1968. |
