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How do combinations of rpsL- and miaA- generate streptomycin dependence?
Abstract:
Petrullo et al. (1983) have studied the consequences of combining a mutation (rpsL-) that normally generates streptomycin resistant (Smr) ribosomes with a mutation (miaA-) that leads to loss of a tRNA hypermodification. They found surprisingly that such doubly mutant bacteria become streptomycin dependent (Smd). Here, we show in vitro that ribosomes purified from an Smr mutant behave very like Smd ribosomes when they are combined with tRNA from an miaA- mutant. Our analysis suggests that proofreading becomes excessively intense when the mutant components are combined, and that this reduces the efficiency of translation to the very low levels characteristic of Smd ribosomes. We show that Sm increases the efficiency of translation in vitro by suppressing the proofreading flows. We suggest that this will explain the growth stimulatory effect of Sm on the rpsL-, miaA- double mutants.
Insights
Combining mutations for streptomycin resistance and tRNA loss unexpectedly caused streptomycin dependence in bacteria. This study reveals that excessive proofreading in these mutants reduces translation efficiency, explaining streptomycin
Area of Science:
- Molecular Biology
- Bacterial Genetics
- Ribosome Function
Background:
- Mutations in rpsL confer streptomycin resistance (Smr) by altering ribosomal proteins.
- Mutations in miaA lead to the loss of tRNA hypermodification, impacting translation fidelity.
- Double mutants (rpsL-, miaA-) exhibit unexpected streptomycin dependence (Smd).
Purpose of the Study:
- To investigate the molecular mechanisms underlying streptomycin dependence in double mutants.
- To elucidate the interplay between ribosomal mutations and tRNA modifications in translation efficiency.
- To understand how streptomycin affects translation in these specific mutant contexts.
Main Methods:
- In vitro reconstitution assays using purified ribosomes and tRNA from mutant strains.
- Analysis of translation efficiency and proofreading dynamics.
- Investigating the effect of streptomycin on in vitro translation.
Main Results:
- Ribosomes from Smr mutants combined with tRNA from miaA- mutants mimicked the behavior of Smd ribosomes.
- Excessive proofreading was identified as the cause of reduced translation efficiency in the double mutants.
- Streptomycin was shown to suppress proofreading, thereby increasing translation efficiency in vitro.
Conclusions:
- The interaction between altered ribosomes and unmodified tRNA leads to hyper-proofreading and translation inefficiency.
- Streptomycin's growth-stimulatory effect on rpsL-, miaA- double mutants is attributed to its ability to suppress this excessive proofreading.
- This study provides a molecular explanation for streptomycin dependence arising from specific genetic combinations.