The 3′‐End of tRNA and Its Role in Protein Biosynthesis

In the course of protein biosynthesis, the 3′‐ends of aminoacyl‐tRNA (aa‐tRNA) and peptidyl‐tRNA specifically interact with macromolecules of the protein biosynthesis machinery. The 3′‐end of tRNA consists of an invariant C‐C‐A single strand. Interaction of the aminoacyl‐tRNA 3′‐end with elongation factor Tu (EF‐Tu) containing bound GTP is necessary for the formation of the aa‐tRNA·EF‐Tu·GTP complex and, after the complex binds to the ribosome, for the GTP hydrolysis. This process is followed by the specific binding of the aminoacyl‐tRNA 3′‐end to the aminoacyl (A) site of the ribosome. In this review, a model is proposed that involves Watson‐Crick base pairing of the CC sequence of the aminoacyl‐tRNA 3′‐end with a specific GG sequence of the ribosomal 23S RNA. Similarly, peptidyl‐tRNA binds with its 3′‐end to the peptidyl (P) site of the ribosome. This binding may also involve Watson‐Crick base pairing of the C‐C‐A sequence with a complementary sequence of 23S RNA. It is proposed that peptide bond formation is catalyzed by a functional site of the 23S RNA located near the 3′‐ends of aminoacyl‐tRNA and peptidyl‐tRNA. A model is suggested in which two loops of the 23S RNA, brought into close proximity via folding, are involved both in binding the 3′‐ends of the tRNAs and in catalyzing peptide bond formation. This model presumes a dynamic structure for ribosomal RNA, which is modulated by interaction with elongation factors and ribosomal proteins.