Studies of the injection of poly(A) + protamine mRNA into Xenopus laevis oocytes

Abstract

When poly(A) + protamine mRNA from trout testes polysomes was injected into living Xenopus oocytes and the latter labelled with [ 14C] or [ 3H]arginine during subsequent incubation, a highly basic, labelled protein fraction was synthesized and could be extracted with 0.5 M H 2SO 4. In the acid extract, a major polypeptide, indistinguishable from trout protamine by several criteria: polyacrylamide and starch gel electrophoreses, carboxymethylcellulose column chromatography, lack of incorporation of [ 3H]histidine, and autoradiography of tryptic peptides after two-dimensional paper electrophoresis, could be demonstrated. Since no such protein is found in control oocytes injected with saline, it is concluded that poly(A) + protamine mRNA programs the synthesis of trout protamine within Xenopus oocytes. This confirms our previous reports [1–3] that trout testis poly(A) + protamine mRNA can direct the in vitro synthesis of protamine in Krebs II ascites, rabbit reticulocytes and wheat germ cell-free systems. The protamine synthesized upon injection of poly(A) + protamine mRNA into Xenopus oocytes appears to be partially phosphorylated. Injection of increasing amounts of poly(A) + protamine mRNA led to a linear increase in protamine synthesis. The sensitivity of detection was such that less than 1 ng of poly(A) + protamine mRNA gave a significant response. The translational stability of protamine mRNA appeared to be less than that of globin mRNA.