Termination

The elongation cycle is repeated until one of the three stop-codons is positioned in the ribosomal A-site. The stop codons have no corresponding tRNAs. Instead, these codons are recognised by a protein, eRF-1 (eukaryotic release factor 1). The activity of eRF-1 is stimulated by eRF-3. The latter is a GTP-binding protein that forms a complex with eRF-1. This complex binds to ribosomes having a stop codon in the A-site. The ribosome-bound complex stimulates the cleavage of the bond (ester bond) between the peptide and the tRNA (peptidyl-tRNA) thereby releasing the new protein from the ribosome. The factors are released from the ribosome following GTP hydrolysis. The ribosome can now start a new translational cycle. In most cases the ribosome initiates a new round of translation on the same mRNA.