Synthesis of a ribosome-bound translatable poly(A)− mRNA during spore germination in Dictyostelium discoideum

Abstract

A distinct poly(A)− RNA sedimenting around 10–12S was identified during spore germination in Dictyostelium discoideum. Activated spores were labeled with [3H]uracil and the poly(A)− RNA was purified from ribosomal particles for analysis. In the spore swelling stage, 40 to 50% of the newly synthesized poly(A)− RNA was 10–12S RNA. This fraction diminished to one-half or one-fourth depending on the labeling period at the stage of amoeba emergence. The 10–12S RNA was associated with both monosomes and polysomes in vivo. Translation in a wheat germ cell-free system and gel electrophoresis demonstrated that the 10–12S RNA coded for a number of polypeptides, some of which were also represented among the in vitro products of poly(A)+ RNA. However, there were seven unique polypeptides (37.5, 28.2, 27.5, 23, 17.7, 17, and 14.2 kilodaltons) encoded exclusively by 10–12S RNA.Key words: cellular slime mold, RNA synthesis, development, poly(A)− mRNA, in vitro translation.