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Published on: February 23, 2021
Ribosomal protein S1 unwinds double-stranded RNA in multiple steps
Xiaohui Qu1, Laura Lancaster, Harry F Noller
1Department of Chemistry, University of California, Berkeley, CA 94720, USA.
Summary
Ribosomal protein S1 unwinds structured messenger RNAs (mRNAs) through a multistep binding process. This mechanism facilitates ribosome initiation on complex mRNA structures, crucial for translation regulation.
Area of Science:
- Molecular Biology
- Biophysics
Background:
- Messenger RNA (mRNA) 5'-end structures regulate translation initiation.
- Ribosomal protein S1 (S1) is vital for translation initiation, especially on structured mRNAs lacking Shine-Dalgarno sequences.
- S1's function is linked to its affinity for single-stranded RNA and destabilization of RNA secondary structures.
Purpose of the Study:
- To elucidate the mechanism by which ribosomal protein S1 interacts with and unwinds RNA secondary structures.
- To quantify the dynamics of S1-mediated RNA unwinding and rezipping using optical tweezers.
Main Methods:
- Utilized optical tweezers techniques to directly measure the force-dependent interactions between ribosomal protein S1 and RNA.
- Analyzed the kinetics of RNA unwinding and rezipping as a function of S1 concentration and applied force.
Main Results:
- Demonstrated that S1 promotes RNA unwinding by binding to transiently formed single-stranded RNA during thermal breathing.
- Showed that S1 dissociation leads to RNA rezipping.
- Quantified S1 binding as a multistep process, with each S1 molecule binding approximately 10 nucleotides of RNA.
- Proposed a model where S1 binding to a 'stand-by site' precedes RNA unwinding, with multistep unwinding being more efficient than single-step unwinding.
Conclusions:
- Ribosomal protein S1 facilitates ribosome initiation on structured mRNAs through a multistep RNA unwinding mechanism.
- The multistep binding and unwinding process significantly enhances the efficiency of overcoming RNA secondary structures compared to single-step models.
- This mechanism provides insight into how S1 plays a critical role in translation regulation and other RNA-related cellular processes.
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