Translational Stop Signals: Evolution, Decoding for Protein Synthesis and Recoding for Alternative Events
Termination or translational stopping involves a close relationship between the ribosome, the mRNA, and the polypeptide chain release factors. The discovery of an array of alternative events occurring at stop codons in the mRNA has focussed attention on how the decoding mechanism discriminates between simple ‘stop’ signals and alternative events outside the normal constraints of the genetic code (Tate and Brown, 1992). This latter phenomenon has been recently called ‘recoding’ and the signals ‘recoding signals’ (Gesteland et al., 1992). Is the normal role of the stop codon merely overriden by the recoding signals or does the stop component of such a signal contribute to a finely tuned regulation at sites where the alternative events occur? These questions demand a re-examination of how a stop signal recognition mechanism might have evolved, first for its function in translational stopping, and second for a possible role in gene regulation.
KeywordsStop Signal Release Factor Alternative Event Nonsense Codon Sense Codon
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