PeptidyltRNA

Peptidyl-tRNA is a transfer RNA molecule carrying a nascent polypeptide chain via an ester bond to its 3' CCA terminus. It is an essential intermediate in the ribosomal elongation cycle of protein synthesis. During the peptidyl transferase reaction, the growing polypeptide that is attached to a tRNA in the P site is transferred to the aminoacyl-tRNA bound in the A site, forming a longer peptidyl-tRNA. After this transfer, the peptidyl-tRNA initially resides in the A site and, following translocation, becomes the tRNA in the P site bearing the peptide. The deacylated tRNA is subsequently moved to the E site and exits the ribosome.

Structurally, the bond linking the polypeptide to the tRNA is a covalent ester linkage between the polypeptide’s carbonyl group and the ribose-attached 3'-adenosine (A76) of the tRNA. This attachment allows the peptide chain to be elongated by successive cycles of aminoacyl-tRNA selection and transfer.

Quality control mechanisms monitor peptidyl-tRNA to ensure translation fidelity. In bacteria and organelles, peptidyl-tRNA hydrolase can hydrolyze peptidyl-tRNA on stalled ribosomes, recycling tRNA and freeing the peptide. Peptidyl-tRNA species also arise in mitochondrial and chloroplast translation, and have corresponding recycling pathways in those organelles.

In summary, peptidyl-tRNA is the substrate for the next peptide bond in translation and serves as a key intermediate that links ribosomal catalysis to polypeptide elongation.