Abstract
During translation, aminoacyl-tRNAs are delivered to the ribosome by specialized GTPases called translation factors. Here, we report the tRNA binding to the P-site of 40 S ribosomes by a novel GTP-independent factor eIF2D isolated from mammalian cells. The binding of tRNA(i)(Met) occurs after the AUG codon finds its position in the P-site of 40 S ribosomes, the situation that takes place during initiation complex formation on the hepatitis C virus internal ribosome entry site or on some other specific RNAs (leaderless mRNA and A-rich mRNAs with relaxed scanning dependence). Its activity in tRNA binding with 40 S subunits does not require the presence of the aminoacyl moiety. Moreover, the factor possesses the unique ability to deliver non-Met (elongator) tRNAs into the P-site of the 40 S subunit. The corresponding gene is found in all eukaryotes and includes an SUI1 domain present also in translation initiation factor eIF1. The versatility of translation initiation strategies in eukaryotes is discussed.
Highlights
Translation initiation in eukaryotes is a complex process involving a number of canonical initiation factors and auxiliary trans-acting proteins
Among the canonical initiation factors, the key role in recruitment of mRNA and delivery of the initiator tRNA onto ribosomes belongs to factors eIF4F and eIF2, respectively, which have no analogs in bacterial cells
As we have recently shown, for those IRES2-containing mRNAs that do not use scanning and deliver their start codons directly to the vicinity of the P-site of the 40 S subunit, the function of Met-tRNAiMet delivery may be accomplished by eIF5B in a way similar to that operating in bacteria [5]
Summary
Translation initiation in eukaryotes is a complex process involving a number of canonical initiation factors and auxiliary trans-acting proteins. We report the tRNA binding to the P-site of 40 S ribosomes by a novel GTP-independent factor eIF2D isolated from mammalian cells.
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