Polysomal and Nonpolysomal Messenger RNA of Noninduced and Induced Friend Erythroleukemic Cells: Analysis by Cell-Free Translation

Abstract

Polyadenylated and nonpolyadenylated mRNA were prepared from polysomes and from the postribosomal supernatant of noninduced and DMSO-induced Friend cells. The mRNA preparations were translated in a wheat germ cell-free system and the in vitro synthesized proteins, fractionated by polyacrylamide gel electrophoresis, were compared by fluorography. The electrophoretic analysis shows that four preparations of poly (A) + RNA code for many different peptides and that most of these peptides are present in each of the poly (A) + RNA translation products. However, the electrophoretic patterns of these translation products differ in the relative amounts of peptides comigrating in the gel electrophoresis. After DMSO treatment, Friend cells show significative differences in the polysomal and nonpolysomal mRNA pools. With induction, globin becomes the most abundant product of the polysomal poly (A) + RNA, while the relative amounts of peptides coded by nonglobin polysomal poly (A) + RNA are reduced. In parallel, the electrophoretic pattern of the in vitro products on the nonpolysomal poly (A) + RNA changes in the relative amounts of the fractionated peptides; moreover, in induced cells, the nonpolysomal poly (A) + RNA codes for peptides not detected in the polysomal poly (A) + RNA of the same cells. These data were interpreted assuming that in DMSO-induced cells, protein synthesis is regulated at both the transcriptional and translational levels. Polysomal poly (A)-RNA codes mostly for the five main histone classes; with DMSO treatment the amount of H2b MRNA bound to polysomes is increased with respect to the other polysomal histone mRNA.