A conformational switch involving the 915 region of Escherichia coli 16 S ribosomal RNA.

A novel alternative conformation, which involves an interaction between the 5' terminal and 915 regions (E. coli numbering), is proposed after a screening of compiled sequences of small subunit ribosomal RNAs. This conformation contains a pseudoknot helix between residues 12-16 and 911-915, and its formation requires the partial melting of the 5' terminal helix and the disruption of the 17-19/916-918 pseudoknot helix of the classical 16 S rRNA secondary structure. The alternate pseudoknot helix is proximal to the binding site of streptomycin and various mutations in rRNA which confer resistance to streptomycin have been located in each strand of the proposed helix. It is suggested that the presence of streptomycin favours the shift towards the alternate conformation, thereby stabilizing drug binding. Mutations which destabilize the novel pseudoknot helix would restrict the response to streptomycin.