NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Riddle DL, Blumenthal T, Meyer BJ, et al., editors. C. elegans II. 2nd edition. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1997.

Cover of C. elegans II

C. elegans II. 2nd edition.

Show details

Section IIThe 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 al. 1994); a 93-amino-acid ribosomal protein (Jones and Candido 1993); numerous tRNAs (Tranquilla et al. 1982; Khosla and Honda 1989; Lee et al. 1990; Schaller et al. 1991; Wilson et al. 1994); tRNA synthetases and modifying enzymes (Gabius et al. 1983; Amaar and Baillie 1993); and translation elongation factor 2 (Ofulue and Candido 1991, 1992) and initiation factor 4A (Roussel and Bennett 1992). An in vitro system of C. elegans translation has unfortunately not yet been developed. C. elegans contains selenocysteine tRNA[Ser]Sec (Lee et al. 1990), a specialized tRNA that inserts selenocysteine (a rare amino acid) in response to specific UGA codons in many organisms. The presence of tRNA[Ser]Sec suggests that some C. elegans UGA codons are not translational terminators. Genes that are expressed highly tend to have greater bias in codon usage than those that are expressed at low abundance (Stenico et al. 1994), although the bias is not as strongly correlated with levels of expression as in yeast (see Appendix 3).

Cytoplasmic translation is noteworthy in that the 5′termini of many mRNAs are added posttranscriptionally by trans-splicing, using either of two different trans-spliced leader sequences (Krause and Hirsh 1987; Huang and Hirsh 1989). Trans-spliced mRNAs retain trimethylguanosine caps of the trans-spliced leader (Liou and Blumenthal 1990). Messages trans-spliced with SL2 are derived from polycistronic precursors (Spieth et al. 1993). It appears that the role of SL2 trans-splicing is to generate monocistronic mRNAs from polycistronic precursors. The role of SL1 trans-splicing is less clear, but SL1 might contribute to efficient translation of SL1-containing mRNAs. For a more thorough review of cis- and trans-splicing in C. elegans, see Blumenthal and Steward (this volume).

B. Mitochondrial Translation

The translational apparatus of C. elegans mitochondria is remarkable in that many of its components are the smallest ever described. The small- and large-subunit rRNAs are the smallest metazoan rRNAs described to date (Okimoto et al. 1994). Models of their secondary structure are remarkably similar to the universal core structures of Escherichia coli 16S and 23S rRNAs. C. elegans mitochondrial tRNAs are also among the smallest known and do not conform to the standard“folded cloverleaf” structure. Instead, 22 mitochondrial sequences are found that can be folded into structures that resemble tRNAs in which the TΨC arm and adjacent variable loop are missing and replaced with a single loop of 6−12 nucleotides (Wolstenholme et al. 1987; Okimoto and Wolstenholme 1990). After 3′-CCA addition, these sequences constitute the complete set of mitochondrial tRNAs (Okimoto et al. 1992). Such tRNAs may represent the smallest adapters capable of functional translation. As in certain other vertebrate and invertebrate mitochondria, the codon AUA specifies methionine (rather than isoleucine in the standard code), UGA specifies tryptophan (rather than stop), and AGA and AGG specify serine (rather than arginine). None of the 12 encoded mitochondrial proteins initiates with the traditional AUG codon. Rather, three initiate with UUG, three with AUA, and six with AUU. Open reading frames terminate with either UAG or UAA. One or both of the“A” residues of UAA terminators are added posttranscriptionally following cleavage and polyadenylation (Okimoto et al. 1990).

Copyright © 1997, Cold Spring Harbor Laboratory Press.
Bookshelf ID: NBK19988
PubReader format: click here to try


  • PubReader
  • Print View
  • Cite this Page

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...