Adaptation fonctionnelle des t-RNA à la biosynthèse protéique dans un système cellulaire hautement différencié: IV — Evolution des t-RNA dans la glande séricigène de Bombyx mori L. au cours du dernier âge larvaire

Abstract

Summary The quantitative changes in the t-RNA species extracted from the post-ribosomal supernatant of the posterior part and of the middle part of the silkgland of Bombyx mori L during the growth phase of the gland and the phase of fibroin and sericin secretion of the 5 th larval instar have been studied. In the posterior part which produces fibroin, the level of t-RNA is increasing 10-fold from the 1 st to the 8 th day and rapidly decreasing during the two days before spinning. In the middle part, which produces sericin similar changes (a continuous 5-fold increase from the 1 st to the 7 th day) are shown. The quantitative changes in each of 17 t-RNA species were followed by in vitro heterologous acylation under optimum conditions. The t-RNA corresponding to the major amino acids of the silk proteins were predominant: t-RNA Ala , t-RNA Gly , t-RNA Ser and t-RNA Tyr in the posterior part, t-RNA Ser , t-RNA Ala , t-RNA Gly and t-RNA Asp in the middle part, account for 2/3 of the total supernatant t-RNA pools at the 8 th day and at the 7 th day respectively. Two groups of t-RNA can be distinguished. Those which have a role in fibroin production, have a maximum concentration at 7–8 days, and those which are primarly involved in the synthesis of other proteins, which reach a maximum around 4–5 days.