Translation in Eukaryotes

The process of translation in eukaryotes is essentially the same as that in bacteria, but differs in several important ways. Structurally, the ribosomal subunits of eukaryotes consist of 40S and 60S subunits that together form an 80S complex. Although most bacterial mRNAs specify multiple proteins, eukaryotic mRNAs code for a single nascent polypeptide chain. However, some newly synthesized polypetide chains may subsequently be enzymatically cleaved into two or more functional protein components.

Only three well-defined initiation factors are required for translation of E. coli mRNAs, but many more are needed in eukaryotes. During initiation, a special initiator tRNA (tRNAiMet) brings an unformylated methionine into the first position on the ribosome. In eukaryotes the 40S ribosomal subunit is thought to attach at the capped 5' terminus rather than at a Shine-Dalgarno sequence as in prokaryotes. It then slides along until it reaches the first AUG start codon. Three different elongation factors in eukaryotes replace those found in bacteria. However, a single release factors acts in eukaryotes.