What signals the termination of translation?

The termination of translation is signaled by the presence of a stop codon. Stop codons, which include UAA, UAG, and UGA, are specific sequences in messenger RNA (mRNA) that do not code for any amino acids. When the ribosome encounters a stop codon during translation, it triggers the release of the newly synthesized polypeptide chain from the ribosome. This process includes the recruitment of release factors that help to disassemble the translation machinery, effectively halting protein synthesis.

In contrast, start codons are important for the initiation of translation, marking where the ribosome should begin synthesizing the protein. High levels of certain amino acids, like tryptophan, can regulate gene expression but are not directly related to the cessation of protein synthesis. The binding of RNA polymerase is involved in the transcription process of synthesizing mRNA, not in the translation phase where polypeptide chains are formed. Thus, the function of stop codons is crucial and specific to ending the translation process.