A Unique tRNA Initiates Protein Synthesis

The translation of every protein begins with the incorporation of the amino acid methionine. A unique initiator tRNA, tRNAjMet, is responsible for the incorporation of this initiating methionine in all protein-synthesizing systems, and it also plays an important role in selecting the appropriate translation start site in mRNA. Generally, only two tRNAs occur in cells that specify methionine. We designate the one that is responsible for the incorporation of internal methio- 

In prokaryotic systems, a specific formylating enzyme exists that can recognize tRNAfMet and formylate, its amino terminus utilizing N1 H-formyItetrahydrofolatc as the formyl donor. This reaction serves to ensure that the initiator does not participate in the elongation reactions. For unknown reasons this recognition step is not possessed by eukaryotic systems. 

The Sequence of the 3 End of E. coli 16S RNA and Some Shine-Dalgarno Sequences at the 5 End of Bacterial mRNAs 

The pyrimidine-rich complement to the Shine-Dalgarno sequence 

The purine-rich The Shine-Dalgarno initiation sequence codon 

---

A Unique tRNA Initiates Protein Synthesis Translation Begins with the Binding of mRNA to the Ribosome... 

---