8 mRNA and Translation

Abstract

I. INTRODUCTION
The process of gene expression, during which the nucleotide sequence of a gene is converted to the amino acid sequence of a protein, is long and tortuous. An expressed gene must be transcribed, its pre-mRNA must be capped, polyadenylated, spliced, and transported to the cytoplasm, and the mature mRNA must be loaded onto polysomes and faithfully translated. In principle, gene expression can be regulated by modulating any of these molecularly complex steps. Indeed, examples of biological regulation occurring at each of these steps have been described in various organisms. We focus in this chapter on translation and translational regulation in Caenorhabditis elegans. Recent work with several C. elegans genes demonstrates that the level, timing, and pattern of gene expression can be regulated at the level of translation by elements contained within a messenger RNA’s 3′-untranslated region (3′ UTR). We also review the genetic and molecular effects of mutations that affect the translational apparatus itself. By altering the mechanics of translation, such mutations can influence the phenotypic consequences of mutations in many different genes.

II. THE TRANSLATIONAL APPARATUS
A. Cytoplasmic Translation
Many components of the translational apparatus have been identified and studied, including ribosomal RNAs and the ribosomal DNA repeat (Sulston and Brenner 1974; Files and Hirsh 1981; Albertson 1984a; Ellis et al. 1986); 5S rRNA and the 5S rDNA repeat (Kumazaki et al. 1982; Nelson and Honda 1985, 1986); ribosomal proteins L29, L21, L35, L37, S9, and S16 (Bektesh et al. 1988; Wilson et al. 1994; Zorio et...