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Characterization of an amber suppressor in Pneumococcus
A M Gasc1, J Vacher, R Buckingham
1Centre de Recherche de Biochimie et de Génétique Cellulaires, C.N.R.S., Toulouse, France.
Molecular & General Genetics : MGG
|January 1, 1979
Summary
A novel suppressor mutation (su+) was identified, partially restoring function in various mutants, including thymidylate synthetase. This amber-specific suppressor offers insights into point mutations.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Mutations can lead to loss of protein function, resulting in altered phenotypes.
- Suppressor mutations can restore function to mutant genes, providing tools to study genetic mechanisms.
- Understanding suppressor mutations aids in characterizing gene function and mutation types.
Purpose of the Study:
- To isolate and characterize a novel suppressor mutation.
- To determine the specificity and mechanism of the identified suppressor.
- To investigate the nature of suppressible mutations using this suppressor.
Main Methods:
- Isolation of a partial revertant with intermediate aminopterin resistance.
- Genetic analysis to identify an unlinked suppressor gene (su+).
- Phenotypic characterization of su+ and its effect on various mutants, including thymidylate synthetase and optochin mutants.
- Transformation experiments with streptomycin resistance allele (str-41).
- Analysis of tRNA from suppressor strains for protein synthesis restoration in bacteriophage f2 amber mutants.
Main Results:
- A suppressor mutation (su+) was identified, unlinked to the amiA locus, conferring intermediate aminopterin resistance and slow growth.
- The su+ mutation suppressed mutations at specific sites within the amiA gene, thymidylate synthetase gene, and optochin resistance locus, indicating site-specificity rather than gene-specificity.
- Thymidylate synthetase activity was partially restored by su+.
- Suppression efficiency was dependent on the mutation site.
- The suppression effect was restricted by the str-41 allele.
- tRNA from the su+ strain restored coat protein synthesis from a bacteriophage f2 amber mutant RNA, suggesting amber-specific suppression.
- Ochre suppression activity was not detected.
Conclusions:
- The su+ gene acts as an informational suppressor, likely targeting amber mutations.
- The site-specific nature of suppression suggests a role in translational fidelity or specific codon recognition.
- The ability of su+ to affect both low and high efficiency mutants supports the hypothesis that these represent point mutations.
- This suppressor provides a valuable tool for studying the nature of suppressible mutations and their impact on protein function.