Structural features of the binding site for ribosomal protein S8 in Escherichia coli 16S rRNA defined using NMR spectroscopy

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Abstract
Ribosomal protein S8 of Escherichia coli plays a key role in 30S ribosomal subunit assembly through its interaction with 16S rRNA. S8 also participates in the translational regulation of ribosomal protein expression through its interaction with spc operon mRNA. The binding site for protein S8 within the 16S rRNA encompasses nucleotides G588 to G604 and C634 to C651 and is composed of two base paired helical regions that flank a phylogenetically conserved core element containing nine residues. We have investigated the structure of the rRNA binding site for S8 both in the free state and in the presence of protein using NMR spectroscopy. The integrity of the two helical segments has been verified, and the presence of G597 x C643 and A596 x U644 base pairs within the conserved core, predicted from comparative analysis, have been confirmed. In addition, we have identified a base triple within the core that is composed of residues A595 x (A596 x U644). The NMR data suggest that S8-RNA interaction is accomplished without significant changes in the RNA. Nonetheless, S8 binding promotes formation of the U598 x A640 base pair and appears to stabilize the G597 x C643 and A596 x U644 base pairs.