Upon irradiation, 3‐[4‐benzoylphenyl]propionyl‐PhetRNA bound to the P‐site of poly(U)‐primed ribosomes is exclusively cross‐linked to 23S RNA. It is shown that the photoreaction only occurs with pyrimidine nucleotides. The site of the cross‐link is located within an 11S RNA fragment, which comprises the 1100 nucleotides at the 3′‐end of 23S RNA. The cross‐linked Phe tRNA derivative is still functionally active in peptide bond formation. The site labelled on the 11S fragment is therefore an integral part of the peptidyltransferase centre.