Characterization of Ribonucleic Acid with Template Activity in Rat Liver Cytoplasm

Abstract

Template activity of RNA from rat liver and the distribution of this activity along a sucrose gradient have been studied. The experiments were performed with RNA extracted from polysomes monosomes and ribosomal subunits. There is no correlation between template activity of RNA extracted from polysomes and early‐labelled RNA, since template activity is distributed all along a sucrose gradient while the radioactivity after a 20 min pulse with [ 14 C]orotic acid is almost exclusively localized in the 18–4 S region. Stimulatory activity in the heavy regions of the gradient is due either to unique large molecules of messenger RNA or to aggregation of ribosomal RNA with messenger RNA. Our experimental results, however, seem to exclude aggregation due to the presence of bivalent ions as well as aggregates held by hydrogen bonds. Ribosomal RNA is itself responsible for part of the template activity found in different fractions of the gradient. Ribosomal RNA extracted from monosomes prepared from polysomes by treatment with RNase, and from subunits, showed a stimulatory activity which, although inferior to that due to messenger RNA, was consistent. Experiments were performed which excluded the possibility that residual messenger still attached to ribosomal RNA was responsible for this activity. Treatment of ribosomal RNA with chemical agents such as EDTA and urea increased the template activity in those cases where a permanent increase in hyperchromicity could be demonstrated. Although neomycin also increased stimulatory activity, it is thought unlikely, on the basis of our experiments, that this is due to a separation of the strands of RNA.