Improved methods for purification and assay of eukaryotic messenger ribonucleic acids and ribosomes. Quantitative analysis of their interaction in a fractionated reticulocyte cell-free system.

The polyadenylic acid-containing messenger ribonucleic acids of eukaryotic cells are rapidly isolated and deproteinized in a simple and gentle one-step procedure. The polyribosome fraction, dissolved in 0.5 M NaCl/0.5 percent sodium dodecyl sulfate, is passed through an oligo(dT)-cellulose column which is then washed with the solvent until proteins and contaminating ribonucleic acids are fully removed. Deproteinized messenger ribonucleic acid is then eluted by lowering the ionic strength. This method gives highly purified and active messenger ribonucleic acids from all tissues tested. The yield is approximately 1.5 to 2 percent of the polyribosomal ribonucleic acid. Messenger ribonucleic acids are assayed in a rabbit reticulocyte-derived, messenger-dependent, cell-free protein-synthesizing system modified from Crystal et al. (Crystal, R. G., Nienhuis, A. W., Elson, N. A., and Anderson, W.F. (1972) J. Biol. Chem. 247, 5357-5368). This system synthesizes proteins at an almost linear rate for at least 2 hours. During this period, each globin messenger ribonucleic acid directs the synthesis of several globin molecules. Each active ribosome synthesizes a globin molecule every 6 to 7 min, but only a small fraction of the ribosomes or messengers are active at any instant. Translation occurs mainly on di- and monoribosomes although larger sized polysomes also occur. Several lines of evidence suggest that globin messenger ribonucleic acid requires "activation" before it can be utilized and that a messenger activation step of protein synthesis initiation is rate-limiting in this cell-free system.