Protected nucleotide G2608 in 23S rRNA confers resistance to oxazolidinones in E. coli

The oxazolidinones are a new class of potent antibiotics that are active against a broad spectrum of Gram-positive bacterial pathogens including those resistant to other antibiotics. These drugs specifically inhibit protein biosynthesis whereas DNA and RNA synthesis are not affected. Although biochemical and genetic studies indicate that oxazolidinones target the ribosomal peptidyltransferase center, other investigations suggest that they interact with different regions of ribosomes. Thus, the exact binding site and mechanism of action have remained elusive. Here, we study, by use of base-specific reagents, the effect of the oxazolidinones on the chemical protection footprinting patterns of the 23S rRNA. We report: (i) reproducible protection of G2607 and G2608 of 23S rRNA by a potent oxazolidinone on a ribosome·tRNA·mRNA complex; (ii) no protections were observed on 70S ribosomes devoid of tRNA and mRNA; (iii) EF-G also weakly protected G2607 and G2608; (iv) mutations at G2608 conferred resistance to the oxazolidinones in Escherichia coli cells; and (v) G2607 and G2608 occur near the exit to the peptide tunnel on the 50S subunit. A mechanism for the pleiotropic action of the oxazolidinones is discussed.