Hyper-accurate ribosomes inhibit growth.

Area of Science:

• Molecular Biology
• Bacterial Genetics
• Antibiotic Resistance Mechanisms

Background:

• Ribosomes are crucial for protein synthesis, and their accuracy is vital for cellular function.
• Mutations conferring streptomycin resistance (SmR), dependence (SmD), or pseudo-dependence (SmP) alter translational fidelity and kinetics.
• Understanding how these mutations affect ribosome function and bacterial growth is key to antibiotic research.

Purpose of the Study:

• To compare in vivo and in vitro translation in wild-type bacteria versus streptomycin-resistant mutants.
• To elucidate the kinetic basis for altered growth rates and translational accuracy in these mutants.
• To investigate the effect of streptomycin on the proofreading activity and translational efficiency of mutant ribosomes.

Main Methods:

• Comparative analysis of in vivo and in vitro translation rates.
• Kinetic experiments using purified ribosomes from wild-type and mutant bacterial strains.
• Measurement of bacterial growth rates in the presence and absence of streptomycin.
• Assessment of ribosome proofreading activities and elongation rates.

Main Results:

• Mutant bacteria (SmR, SmD, SmP) exhibit slower and more accurate translation than wild-type bacteria, particularly in the absence of streptomycin.
• Streptomycin-pseudo-dependent (SmP) bacteria show significantly reduced growth rates compared to wild-type.
• Streptomycin stimulates growth and translation rates in SmP mutants by reducing ribosome proofreading and increasing elongation rates.
• Mutant ribosomes display more rigorous proofreading activities, leading to reduced kinetic efficiency and slower growth.

Conclusions:

• Excessively accurate ribosomes in streptomycin-resistant mutants are kinetically less efficient, inhibiting growth.
• Streptomycin enhances the growth of these mutants by decreasing proofreading, thereby increasing translational efficiency.
• The loss of proofreading activity, despite a potential loss of accuracy, is beneficial for mutant growth in the presence of streptomycin.