Translation in eukaryotes

The mDHFR protein complementation assay has been used to map a signal transduction network that controls the initiation of translation in eukaryotes (Remy and Michnick, 2001). A total of 35 different pairs of full-length proteins were analyzed and 14 interactions were identified using the survival selection of cells grown in the absence of nucleotides. In addition, the use of the fMTX reagent in combination with fluorescence microscopy was used to localize the protein complex within cells (Remy and Michnick, 2001). 

Yusupov MM, Yusupova GZ, Baucom A, Lieberman K, Earnest TN, Cate JH, Noller HF (2001) Crystal structure of the ribosome at 5.5A resolution. Science 292 883—896 Zhouravleva G, Frolova L, Le Goff X, Le Guellec R, Inge-Vechtomov S, Kisselev L, Philippe M (1995) Termination of translation in eukaryotes is governed by two interacting polypeptide chain release factors, eRFl and eRF3. EMBO J 14 4065-4072... 

Hershey, J. W. B., Protein phosphorylation controls translation rates. J. Biol. Chem. 264 20823, 1989. Describes how protein kinases are thought to regulate translation in eukaryotic systems. 

The elongation stage of translation in eukaryotes requires three elongation factors, eEFla, eEFI[3y and eEF2, which have similar functions to their prokaryotic counterparts EF-Tu, EF-Ts and EF-G (see Table 1). 

Translation in prokaryotes (H2) Protein glycosylation (H5) Translation in eukaryotes (H3)... 

The molecular mechanism of translation in eukaryotes is very similar to that in bacteria. The activation of amino acids and attachment to tRNAs and the steps of initiation, elongation, and termination of polypeptide chains are essentially the same in overall terms. The small and large ribosomal subunits of bacteria and eukaryotes are equivalent with respect to their roles in initiation and elongation of chains. 

The translation of mRNA to protein concludes the gene expression cascade and links the proteome to the genome. Consequently, control of translation can be a direct and effective means to modulate the proteome [21, 30, 31]. In addition to transcript interactions with protein regulators, translation is also modulated by structural features or regulatory sequences appearing within the mRNA molecules. The 7-methylguanylate triphosphate nucleotidyl caps at the 5 end, poly-A tails, uORFs, and IRESs are examples of structures that affect the rate and efficiency of translation in eukaryotes [21]. 

Lapointe, J. Giegd, R. (1991). Transfer RNAs and aminoacyl-tRNA synthetases. In Translation in Eukaryotes. (Trachsel, H., ed.), pp. 35-69, CRC Press, Boca Raton. 

The Kozak model for the initiation of translation in eukaryotes [89] states that the ribosome scans along the 5 untranslated region of an mRNA until it selects a translation start codon to initiate translation. Selection of an AUG codon to start translation requires a favorable environment, which can be described by the gen-... 

The previous sections have introduced the major participants in protein synthesis—mRNA, aminoacylated tRNAs, and ribosomes containing large and small rRNAs. We now take a detailed look at how these components are brought together to carry out the biochemical events leading to formation of polypeptide chains on ribosomes. Similar to transcription, the complex process of translation can be divided into three stages—initiation, elongation, and termination—which we consider in order. We focus our description on translation in eukaryotic cells, but the mechanism of translation is fundamentally the same in all cells. 

In addition to mRNA and tRNA, the third major class of RNA molecule required for protein synthesis is rRNA. Together with as many as 70 ribosomal proteins, rRNA folds into a two-subunit macromolecule complex called a ribosome (Chapter 5). In bacteria, the ribosomes attach to mRNA as it is being synthesized, thereby coupling transcription and translation. In eukaryotes, protein synthesis occurs in the cytoplasm, either by free ribosomes in the cytosol or by membrane-bound ribosomes associated with the endoplasmic reticulum. The differences between prokaryotic and eukaryotic protein synthesis are illustrated in Figure 26.3. 

A critical consideration for N-terminal modification strategies is the ease with which the identity of the first amino acid can be established. Although all proteins begin with methionine as the first amino acid due to the commonality of the AUG start codon, this group is nearly always removed after translation in eukaryotes. The situation is more complicated in prokaryotes, however, as the methionyl aminopeptidases are sensitive to the size of the second amino... 

Each mRNA molecule contains a nucleotide sequence that is converted into the amino acid sequence of a polypeptide chain in the process of translation. In eukaryotes, messenger RNA (mRNA) is transcribed from protein-coding genes as a long primary transcript that is processed in the nucleus to form mRNA. The various processing intermediates, which are mRNA precursors, are called pre-mRNA or hnRNA (heterogenous nuclear RNA). mRNA travels through nuclear pores to the cytoplasm, where it binds to ribosomes and tRNAs and directs the sequential insertion of the appropriate amino acids into a polypeptide chain. 

---