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Optimization of a ribosomal structural domain by natural selection
Corina Maeder1, Graeme L Conn, David E Draper
1Program in Molecular and Computational Biophysics and Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Biochemistry
|May 24, 2006
Summary
The stability of a ribosomal RNA domain in Escherichia coli is sufficient for function, suggesting evolutionary pressures, not structural limits, shape its current form. Minor stability variations do not impact cell growth.
Area of Science:
- Molecular Biology
- Structural Biology
- Evolutionary Biology
Background:
- A conserved domain in the large ribosomal subunit comprises rRNA and protein L11.
- The Escherichia coli rRNA fragment shows marginal in vitro stability, unlike stabilized variants in other organisms.
Purpose of the Study:
- Investigate why natural selection hasn't favored a more stable rRNA structure in E. coli.
- Assess the in vitro and in vivo effects of mutations on rRNA stability and L11 binding.
Main Methods:
- Assessed in vitro rRNA fragment stability and L11 affinity.
- Evaluated in vivo effects on cell growth rate and ribosome L11 content.
Main Results:
- rRNA fragment stabilities varied from -4 to +9 kcal/mol.
- Mutations with stabilities from -4 to +5 kcal/mol had minimal in vivo effects.
- Destabilizing mutations exceeding -7 kcal/mol were not tolerated.
- Estimated in vivo complex stability is approximately -6 kcal/mol.
Conclusions:
- Individual tertiary interactions are dispensable if minimum complex stability is maintained.
- Evolution of this ribosomal domain is not limited by inherent stability constraints.
- Small selective advantages for increased stability may be outweighed by other evolutionary pressures.