Mechanism and regulation of translation in C. elegans.

C. elegans represents a favorable system to study the extraordinarily complicated process of eukaryotic protein synthesis, which involves over 100 RNAs and over 200 polypeptides just for the core machinery. Initial research in protein synthesis relied on fractionated mammalian and plant systems, but in the mid-1970s, the powerful genetics of Saccharomyces cerevisiae began to yield new insights for translation in all eukaryotes. C. elegans has many features of higher eukaryotes that are not shared by yeast. This allows protein synthesis researchers to combine biochemistry, cell biology, developmental biology, genetics, and genomics to study regulation of gene expression at the translational level. Most components of the core translational machinery have been identified in C. elegans, including rRNAs, 5S RNA, tRNAs, ribosomal proteins, and aminoacyl tRNA synthetases. C. elegans has amino acid sequence homologs for 56 of the known initiation, elongation, and release factor polypeptides, but few of these have been isolated, functionally identified, or studied at the biochemical level. Similarly, C. elegans has homologs for 22 components of the major signal transduction pathways implicated in control of protein synthesis. The translational efficiency of individual mRNAs relies on cis-regulatory elements that include either a 7-methylguanosine- or 2,2,7-trimethylguanosine-containing cap, the 5'-terminal spliced leader, sequence elements in the 3'-untranslated regions, and the 3'-terminal poly(A) tract. Several key developmental pathways in C. elegans are predominantly governed by translational mechanisms. Some evidence has been presented that well described regulatory mechanisms in other organisms, including covalent modification of translation factors, sequestration of translation factors, and mRNA-specific changes in poly(A) length, also occur in C. elegans. The most interesting unexplored questions may involve changes in the translation of individual mRNAs during development, in response to physiological changes, or after genetic manipulations. Given the highly developed state of C. elegans genomics, it can be expected that future application of computational tools, including data visualization, will help detect new instances of translational control.