Ribosomes from Xenopus laevis eggs and embryos in a cell-free protein-synthesizing system: translational regulation

Abstract

Three types of ribosomal preparations from Xenopus laevis eggs and embryos were tested in a cell-free system to study possible translational regulation of protein synthesis as mediated by the ribosome during early amphibian development: type I, a crude high-speed sediment, mainly containing monoribosomes completely dissociable by 0.5 M KCl, type II, ribosomes washed with 0.5 M KCl; and type III, ribosomes treated with puromycin—0.5 M KCl. All three types showed an active response to the addition of poly [U]. Type III was found to be the most active: levels of incorporation of 30 phenylalanine residues/ribosome were reached. In all three cases ribosomes prepared from unfertilized eggs were 30–40% less active in vitro than those from cleavage and gastrula stages.