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Mutations in 16S rRNA that affect UGA (stop codon)-directed translation termination
H U Göringer1, K A Hijazi, E J Murgola
1Max-Planck-Institut für Molekulare Genetik, Abteilung Wittmann, Berlin, Federal Republic of Germany.
Abstract:
Site-directed mutagenesis was performed on a sequence motif within the 3' major domain of Escherichia coli 16S rRNA shown previously to be important for peptide chain termination. Analysis of stop codon suppression by the various mutants showed an exclusive response to UGA stop signals, which was correlated directly with the continuity of one or the other of two tandem complementary UCA sequences (bases 1199-1204). Since no other structural features of the mutated ribosomes were hampered and the translation initiation and elongation events functioned properly, we propose that a direct interaction occurs between the UGA stop codon on the mRNA and the 16S rRNA UCA motif as one of the initial events of UGA-dependent peptide chain termination. These results provide evidence that base pairing between rRNA and mRNA plays a direct role in termination, as it has already been shown to do for initiation and elongation.
Insights
Mutagenesis of Escherichia coli 16S rRNA
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Peptide chain termination is a critical process in protein synthesis.
- The 3' major domain of Escherichia coli 16S rRNA is implicated in termination.
- Previous studies suggested a role for rRNA in termination signals.
Purpose of the Study:
- To investigate the role of a specific sequence motif in Escherichia coli 16S rRNA in peptide chain termination.
- To elucidate the mechanism of UGA stop codon recognition during termination.
Main Methods:
- Site-directed mutagenesis was used to alter the 16S rRNA sequence motif.
- Analysis of stop codon suppression in mutant ribosomes was performed.
- Ribosome function, including initiation and elongation, was assessed.
Main Results:
- Mutations exclusively affected UGA stop signal recognition.
- The UGA response correlated with the integrity of tandem UCA sequences (bases 1199-1204).
- Ribosome initiation and elongation remained functional in mutants.
Conclusions:
- A direct interaction between the UGA stop codon and the 16S rRNA UCA motif is proposed for UGA-dependent termination.
- Base pairing between rRNA and mRNA plays a direct role in peptide chain termination.
- This interaction is a key event in initiating UGA-dependent peptide chain termination.