The majority of calf muscle cell messenger RNAs contain poly(A)

Abstract

Previous studies from our laboratory have investigated messenger RNA metabolism in calf muscle cells in tissue culture. The analysis of mRNA was based on its poly(A) content. We have now examined directly the proportion of mRNA which contains poly(A) in these cells. After separation of poly(A) +- and poly(A) −-RNA on oligo(dT)-cellulose, the two fractions were translated in a reconstituted, heterologous cell-free protein-synthesizing system and the products were compared with those from the translation of total RNA. The great majority of mRNA form either prefusion or postfusion cultures was poly(A)-containing; quantitative determinations show that about 70–90% of the actin mRNA is poly(A)-containing. In order to determine if a large fraction of the calf muscle mRNA can be translated by a heterologous cell-free system, [ 3H]-poly(A) +-RNA was added to reticulocyte lysates and the formation of initiation complexes was followed. These experiments suggest that the bulk of calf muscle cell mRNA would be utilized in such a system and justify the use of cell-free systems to examine the poly(A) content of total mRNA. Thus, differential polyadenylation does not seem to be an important aspect of mRNA metabolism in cultured muscle cells. The previous study of mRNA in these cells, based on poly(A) content, is apparently a valid measure of overall mRNA metabolism.