THE 5' PROXIMAL HELIX OF 16S RIBOSOMAL-RNA IS INVOLVED IN THE BINDING OF STREPTOMYCIN TO THE RIBOSOME

Single mutations at the end of the 5' proximal helix and in the 915 region (13U --> A or C; 914A --> U or G), and double mutations (13U --> A and 914A --> U; 13U --> C and 914A --> G) were constructed into Escherichia coli 16S ribosomal RNA. The mutations were introduced into an expression plasmid containing the rrnB operon under the transcriptional control of the temperature-inducible lambdaP(L) promoter. None of the mutant 16S rRNAs affected cell growth when expressed. Ribosomes extracted after induction of expression of the mutant 16S rRNAs were assayed for their capacity to bind the error-inducing drug streptomycin and for translational misreading in the presence of streptomycin. All mutations impaired the binding of streptomycin, and consequently its capacity to stimulate misreading. Our results demonstrate the involvement of the 5' proximal helix of 16S rRNA in the binding of streptomycin and confirm the participation of the 915 region. They do not support a previous suggestion [Leclerc, D. and Brakier-Gingras, L. (1991) FEBS Lett., Vol. 279, pp. 171-174] that base pairing between nucleotides 13 and 914 stabilizes the binding of streptomycin.