A detailed view of a ribosomal active site: The structure of the L11-RNA complex

We report the crystal structure of a 58 nucleotide fragment of 23S ribosoma l RNA bound to ribosomal protein L11. This highly conserved ribonucleoprote in domain is the target for the thiostrepton family of antibiotics that dis rupt elongation factor function. The highly compact RNA has both familiar a nd novel structural motifs. While the C-terminal domain of L11 binds RNA ti ghtly, the N-terminal domain makes only limited contacts with RNA and is pr oposed to function as a switch that reversibly associates with an adjacent region of RNA. The sites of mutations conferring resistance to thiostrepton and micrococcin line a narrow cleft between the RNA and the N-terminal dom ain. These antibiotics are proposed to bind in this cleft, locking the puta tive switch and interfering with the function of elongation factors.