13 Translational Control of Ribosomal Protein mRNAs in Eukaryotes

Abstract

Many complex processes that occur during normal growth, differentiation, development, or malignant transformation in eukaryotes involve regulation of ribosome biosynthesis. This organelle contains four species of ribosomal RNA and more than 70 different ribosomal protein molecules, all of which appear in equimolar amounts (for review, see Wool et al., this volume). Thus, to maintain the proper stoichiometry of the ribosomal components at varying cellular growth rates, there must be regulatory mechanisms to ensure both coordinate synthesis of all ribosomal components and modulated formation of ribosomes.

The equimolar accumulation of ribosomal proteins is maintained by coordinate regulation at various levels of gene expression (Meyuhas et al. 1987; Aloni et al. 1992 and references therein). It seems, however, that under many physiological conditions, control of ribosomal protein gene expression at the translational level is the most prevalent regulatory mechanism operating in both eukaryotes and prokaryotes. Interestingly, the synthesis of ribosomal proteins in yeast is generally not regulated at the translational level (Tsay et al. 1988), with the exception of a single documented case (Dabeva and Warner 1993).

This chapter focuses on the translational control of messenger RNAs encoding both ribosomal proteins and several related proteins during development, with fluctuations in growth rate and upon hormonal stimulation, as studied in various eukaryotic organisms and cell lines. Alterations in the translational efficiency of these mRNAs appear to be of a selective nature, to be coregulated with the accumulation of rRNA, and to involve the 5′-untranslated region (5′ UTR) as the cis-regulatory element.

GROWTH-DEPENDENT TRANSLATIONAL...