Ribosomal protein S1 is an RNA-binding ribosomal protein that helps many bacterial messenger RNAs engage the small ribosomal subunit for translation initiation. In Escherichia coli, S1 is a single polypeptide chain containing six related S1 RNA-binding domains. The whole protein and its repeated domain are distinct concepts; an S1 domain also occurs in proteins outside the ribosome.[ref]
Escherichia coli Ribosomal Protein S1 Unfolds Structured mRNAs Onto the Ribosome for Active Translation Initiation by Mélodie Duval and others. Introduction, E. coli S1 architecture
[ref]A 2013 study tested how S1 helps structured messages enter the decoding region. Researchers compared intact, S1-depleted and reconstituted 30S subunits, including S1 variants missing selected domains. Binding measurements and toeprinting distinguished RNA association from formation of a correctly positioned 30S initiation complex. The experiments showed different domain requirements for different messages; the first three domains were important for handling the tested structured rpsO message.[ref]
Escherichia coli Ribosomal Protein S1 Unfolds Structured mRNAs Onto the Ribosome for Active Translation Initiation by Mélodie Duval and others. Figures 3–4 and Figure S5, domain deletions and initiation-complex comparisons
For an illustrative control, suppose removing S1 reduces an initiation-associated signal for a folded message but changes a simpler message little. Restoring the signal by adding back intact S1 would support a message-dependent contribution. General loss of ribosome assembly or unequal RNA amounts could also change the readout, so they require separate checks. An RNA-binding measurement alone does not establish completed translation; a domain count alone does not specify how many functional binding sites a protein supplies.
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