The ribosomal peptidyl transferase center is a ribozyme catalyzing peptide bond synthesis in all organisms. We applied a novel modified nucleoside interference approach to identify functional groups at 9 universally conserved active site residues. Owing to their immediate proximity to the chemical center, the 23S rRNA nucleosides A2451, U2506 and U2585 were of particular interest. Our study ruled out U2506 and U2585 as contributors of vital ...