| Abstract: | It is demonstrated that RNA isolated from polyribosomes and postmitochondrial fraction of rat liver cells and bound to nitrocellulose filters (Milliport) represent mRNA. RNA taken from the nitrocellulose filters sedimented in sucrose concentration gradient with a wide peak within the range of 18--6S, attaining a maximum at 12S. The (A+U)/(G+C) ratio of this RNA was equal to 1.04. On the other hand, the same ratio for rRNA was 0.64. Specific radioactivity of polysomal mRNA containing poly-A sequences, was significantly lower at 14-hour labelling with 14C-orotate than at 4-hour labelling (control). Inhibitors (cycloheximide, puromycin, ethionine, actinomycin D) stabilized polysomal mRNA. Specific radioactivity of postmitochondrial fraction mRNA was higher at 14-hour labelling than at 4-hour labelling. Specific radioactivity of postmitochondrial fraction mRNA during protein synthesis blocking by different inhibitors was comparable to those of control animals. It is hypothesized that active translation is necessary for the initiation of rat liver mRNA degradation. |
