DECODING THE TRANSLATIONAL TERMINATION SIGNAL - THE POLYPEPTIDE-CHAINRELEASE FACTOR IN ESCHERICHIA-COLI CROSS-LINKS TO THE BASE FOLLOWING THE STOP CODON

Protein release factors act like tRNA analogues in decoding translatio nal stop signals. Statistical analysis of the sequences at translation al stop sites and functional studies with particular signals indicate this mimicry involves an increase in the length of the signal in the m RNA. The base following the stop codon (+4 base) is of particular inte rest because it has a strong influence on the competitiveness of the s top signal at recoding sites, suggesting it might form part of the rel ease factor recognition element. Site-directed crosslinking from the 4 base showed that it is in close proximity to the Escherichia coli re lease factor-2 in a termination complex, a prerequisite for the +4 bas e being part of the recognition element. Fingerprinting analysis indic ates that crosslinking to the release factor occurred from both +1 and +4 positions of the stop signal in the same RNA molecule. This provid es more evidence that the +4 base may be an integral part of the decod ing signature in the mRNA during the termination phase of protein bios ynthesis.