Initiator tRNAs and Initiation of Protein Synthesis

Abstract

Initiation of protein synthesis occurs universally with the amino acid methionine or its derivative formyl methionine. Of the two classes of methionine tRNAs present in all organisms, the initiator is used for initiation of protein synthesis, whereas the elongator is used for insertion of methionine into internal peptidic linkages. In eubacteria and in eukaryotic organelles such as chloroplasts and mitochondria, the initiator tRNAs are used as formylmethionyl-tRNA (fMet-tRNA). In the cytoplasmic protein synthesis system of eukaryotes and in archaebacteria, they are used as methionyl-tRNA (Met-tRNA) without formylation. This chapter focuses on initiator tRNAs and their role in initiation of protein synthesis. It provides a brief and somewhat simplified description of some of the steps of protein synthesis initiation that involve the initiator tRNA most directly. Then, it describes the special properties of eubacterial and eukaryotic initiator tRNAs and the current knowledge of the relationship between the sequence and structure of the initiator tRNAs and their function.