Changes in codon recognition and chromatographic behaviour of tRNA species during embryonic development of the sea urchin Paracentrotus lividus

14C- or 3H-aminoacyl-tRNA from fertilized eggs and from embryos at the pluteus stage were analyzed by chromatography on benzoylated DEAE cellulose columns. Differences in the chromatographic species between the two stages were found for lysyl- arginyl- and leucyl-tRNA. No differences were observed for valyl- and seryl-tRNA. Leucine, lysine, serine and arginine tRNA from both stages of development were tested for codon recognition by the ribosomal binding technique. At the pluteus stage, the binding to ribosomes of lysyl-tRNA is about five fold higher in the presence of poly AG than in the presence of poly A, whereas the difference is only two fold in fertilized eggs. Poly AG stimulates the binding of arginyl-tRNA from both stages. At 0.02 M Mg+2 the stimulation is increased in pluteus tRNA while it is decreased in the tRNA of fertilized eggs. Moreover at this magnesium concentration the binding of pluteus arginyl-tRNA is stimulated by poly G. Less remarkable quantitative differences in codon recognition between the two stages were observed for seryl-tRNA, while the codon recognition by leucyl-tRNA does not vary during development.