Decoding the translational termination signal: the polypeptide chain release factor in Escherichia coli crosslinks to the base following the stop codon.

Protein release factors act like tRNA analogues in decoding translational stop signals. Statistical analysis of the sequences at translational stop sites and functional studies with particular signals indicate this mimicry involves an increase in the length of the signal in the mRNA. The base following the stop codon (+4 base) is of particular interest because it has a strong influence on the competitiveness of the stop signal at recoding sites, suggesting it might form part of the release factor recognition element. Site-directed crosslinking from the +4 base showed that it is in close proximity to the Escherichia coli release factor-2 in a termination complex, a prerequisite for the +4 base being part of the recognition element. Fingerprinting analysis indicates that crosslinking to the release factor occurred from both +1 and +4 positions of the stop signal in the same RNA molecule. This provides more evidence that the +4 base may be an integral part of the decoding signature in the mRNA during the termination phase of protein biosynthesis.