Translation of partially purified poly(A)+ protamine messenger RNA components in wheat germ and rabbit reticulocyte cell-free systems. Evidence for translational control mechanisms

Abstract

The coding properties of individual poly(A)+ protamine mRNA subcomponents have been explored by analysis of their translation products in two different cell-free protein synthesis systems, the rabbit reticulocyte lysate and the wheat germ S-30, both of which can translate total protamine mRNA. The products synthesized in the reticulocyte lysate in the presence of total poly(A)+ PmRNA consisted mainly of protamine components CII and CIII with component CI only a minor product. However, in the wheat germ S-30, the same mRNA preparation supported the synthesis of all three protamine components, in approximately equal amounts. In addition a new polypeptide, a putative fourth protamine component, labelled CO, was also synthesized. The translation products of subcomponents of poly(A)+ PmRNA separated as individual bands on polyacrylamide gels were similarly analyzed and it was shown that each of the isolated poly(A)+ PmRNA species could stimulate the incorporation of [3H]arginine into protamines in both translational systems. Although each mRNA band stimulated the synthesis of one particular protamine polypeptide predominantly in a given cell-free system, the same RNA preparation was found to direct preferentially the synthesis of a different protamine component in the second cell-free system. The products synthesized in the rabbit reticulocyte lysate in the presence of the individual mRNA species still showed component CI present as a minor product.