par Levis, Angelo Gino;Krsmanovic, Velibor;Errera, Maurice Leo
Référence Biochimica et biophysica acta, N. Nucleic acids and protein synthesis, 145, 3, page (577-595)
Publication Publié, 1967-10
Article révisé par les pairs
Résumé : The nucleic acids of HeLa cells, labelled for 30 min with [3H]uridine are extracted by sodium dodecylsulphate-chloroform-isoamylalcohol and fractionated on methylated bovine serum albumin adsorbed on kieselguhr (MAK) columns and by Cs2SO4 density gradient centrifugation. A DNA-RNA complex is described which involves a fraction of labelled RNA resistant to ribonuclease at conditions which distinguish hybridized from free RNA. This complex is dissociated, like DNA-RNA hybrids, by heat treatment and does not appear to be an artificial association formed between DNA and non-specific RNA at the moment of cell lysis or during any of the subsequent biochemical steps. The heat dissociated RNA sediments in sucrose gradients with a peak at about 4-6 S, no radioactivity being detected in the heavy regions of the gradients. The limited size of these molecules is tentatively attributed to their breakage during extraction, or to their degradation due to the heat treatment used to free them from DNA. The true hybridized, ribonuclease-resistant structures appear to consist of short sequences of newly synthesized RNA, containing about 20-40 nucleotides. The RNA bound to the DNA at the time of extraction is of the order of 0.35 % of the total RNA synthesized during a 30-min incubation (this is probably a minimum value), and the proportion of DNA carrying such a fraction of RNA is about 0.03 %. © 1967.