What happens to the translation components during the termination phase?

Sourav PanNovember 9, 2024

Answered

During the termination phase of translation, several key events occur that lead to the release of the newly synthesized polypeptide and the disassembly of the translation components. Here’s a detailed overview of the process:

Key Events in Translation Termination

1. Recognition of Stop Codon:
   • Termination begins when a stop codon (UAA, UAG, or UGA) enters the A site of the ribosome. Stop codons do not code for any amino acids and signal the end of translation.
2. Binding of Release Factors:
   • In response to the presence of a stop codon, specific proteins known as release factors (RFs) bind to the ribosome. In prokaryotes, there are two primary release factors: RF1 and RF2, which recognize different stop codons. In eukaryotes, a single release factor, eRF1, recognizes all three stop codons with the help of eRF3, which is a GTPase that enhances the termination process.
3. Peptide Release:
   • Once the release factor is bound, it catalyzes the hydrolysis of the bond between the nascent polypeptide chain and the tRNA in the P site. This reaction involves adding a water molecule instead of an amino acid, leading to the release of the completed polypeptide from the ribosome. The nascent peptide exits through the ribosomal exit tunnel.
4. Dissociation of Ribosomal Subunits:
   • After peptide release, the ribosome undergoes conformational changes that facilitate its disassembly into its constituent subunits (small and large subunits). In prokaryotes, this process is assisted by additional factors such as ribosome recycling factor (RRF) and elongation factor G (EF-G), which help separate the subunits and release any remaining tRNA . In eukaryotes, this process is mediated by proteins like ABCE1 that promote dissociation .
5. Release of tRNA and mRNA:
   • The deacylated tRNA (the tRNA without an attached amino acid) is released from the P site. Additionally, any remaining mRNA is also released from the ribosome during this process . The disassembly allows for recycling of these components for future rounds of translation.
6. Post-Termination Complex:
   • After termination, a post-termination complex may form briefly before complete disassembly occurs. This complex ensures that all components are properly recycled and can participate in new rounds of translation