Distinct functional classes of ram mutations in 16S rRNA

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The ribosome accurately translates genetic code via a two-stage decoding process involving initial selection and proofreading.
• Ribosomal ambiguity (ram) mutations in 16S rRNA have been previously identified, suggesting specific ribosomal regions are critical for decoding fidelity.
• Understanding these mutations is key to elucidating the intricate mechanisms governing translation accuracy.

Purpose of the Study:

• To investigate the functional impact of specific ram mutations on the ribosome's decoding process.
• To differentiate the effects of mutations in distinct ribosomal regions on initial selection, proofreading, and overall translation fidelity.
• To correlate mutation location with miscoding phenotypes and their dependence on codon-anticodon interactions.

Main Methods:

• Analysis of a subset of previously isolated ram mutations in 16S rRNA.
• Assessment of mutation effects on initial selection and proofreading stages of aminoacyl-tRNA (aa-tRNA) binding.
• Evaluation of miscoding frequencies in various contexts, including RF2-dependent termination.
• Characterization of codon-anticodon-dependent phenotypes.

Main Results:

• Mutations disrupting inter-subunit bridge B8 generally increased miscoding by impairing both initial selection and proofreading.
• Mutations located in or near the ribosomal A site exhibited context-dependent increases in miscoding.
• These A site mutations appear to facilitate spurious interactions with near-cognate aa-tRNAs.

Conclusions:

• Ribosomal structure, particularly inter-subunit bridges and the A site, plays a crucial role in maintaining translation fidelity.
• Distinct ribosomal regions contribute differentially to decoding accuracy, with A site mutations causing context-specific errors.
• The findings provide mechanistic insights into how ribosomal mutations can lead to context-dependent translation errors.