Compensatory evolution reveals functional interactions between ribosomal proteins S12, L14 and L19

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Mutations in ribosomal protein S12 can confer streptomycin resistance.
• Compensatory mutations in ribosomal proteins S4, S5, and L19 can mitigate the fitness cost of S12 mutations.
• The specific in vivo roles of L19 mutations in fitness, translation speed, and accuracy remain largely uncharacterized.

Purpose of the Study:

• To characterize the in vivo fitness, translation speed, and accuracy of L19 mutants.
• To investigate the compensatory potential of L19 mutations in the context of S12-mediated streptomycin resistance.
• To explore the functional implications of L19 mutations on bacterial growth and protein synthesis.

Main Methods:

• In vivo characterization of four L19 mutants (Q40H, Q40L, Q40R, G104A).
• Assessment of bacterial growth rates and fitness.
• Measurement of protein synthesis rates and translational accuracy (UGA nonsense codon read-through).
• Evolution experiments involving serial passage of low-fitness L19 mutants.

Main Results:

• L19 mutations at position 40 (Q40H, Q40L, Q40R) decreased fitness, while G104A had no effect.
• Mutations at position 40 affected translational accuracy by increasing UGA read-through, indicating a loss of accuracy.
• L19 mutations increased sensitivity to A-site aminoglycosides, suggesting decoding step perturbation.
• Compensatory mutations for L19 fitness costs were found in L19, S12, and L14.

Conclusions:

• The 50 S ribosomal protein L19 plays a novel role in protein synthesis, influencing translation accuracy and fitness.
• L19 mutations can perturb the ribosomal decoding step, similar to classical ram mutants.
• Compensatory evolution is a valuable tool for uncovering new molecular functions of ribosomal proteins.