BIOCHEMICAL-RESEARCH ON OOGENESIS - AMINOACYL TRANSFER-RNA TURNS OVER IN THE 42-S PARTICLES OF XENOPUS-LAEVIS OOCYTES, BUT ITS ESTER BOND IS PROTECTED AGAINST HYDROLYSIS

The ester bond of aminoacyl tRNA is protected against hydrolysis in the 42-S particles (thesaurisomes) present in X. laevis previtellogenic oocytes. Deacylation of tRNA is very slow in vitro, unless ATP is present. ATP causes a partial turnover of aminoacyl tRNA in vitro, with no detectable decrease in the overall aminoacylation level of tRNA, which remains close to 100%. tRNA in the particles turns over rapidly in vivo. Since the ester bond of aminoacyl tRNA is stabilized inside the 42-S particles, this turnover cannot be a consequence of spontaneous deacylation of tRNA, followed by reacylation by the aminoacyl-tRNA synthetases associated with the particles. This turnover is considered as reflecting a true metabolic activity of the particles and a direct or indirect involvement of these particles in the oocyte''s protein-synthesizing system.