Relationship between rates of synthesis and intracellular distribution of ribosomal proteins during oogenesis in the mouse.

Ribosomal proteins are synthesized continuously in nonequimolar amounts during oogenesis in the mouse (M. J. LaMarca and P. M. Wassarman, 1979, Develop. Biol. 73, 103), even though ribosomal proteins are found in equimolar amounts in ribosomes. In this report, the distribution of newly synthesized ribosomal proteins between the cytoplasm and germinal vesicle (nucleus) of fully grown mouse oocytes has been examined. As compared to total newly synthesized protein, ribosomal proteins were found to be highly concentrated in the oocyte's germinal vesicle. Furthermore, an inverse relationship was found between rates of synthesis of individual ribosomal proteins and percentages of newly synthesized ribosomal proteins associated with germinal vesicles. As a result of this relationship, the amounts of newly synthesized ribosomal proteins associated with germinal vesicles approximated an equimolar situation. Even in the presence of actinomycin D, oocytes continued to synthesize ribosomal proteins which were found associated with germinal vesicles in amounts similar to those observed in the absence of the drug. These results suggest that, although synthesis of ribosomal proteins by mouse oocytes is not coordinately regulated, a post-translational mechanism exists for adjusting the stoichiometry of these proteins within the oocyte's germinal vesicle; this mechanism apparently is not dependent upon concomitant ribosomal-RNA synthesis.