Ribosomal RNA‐protein cross‐links, induced by γ‐irradiation of 40S and 60S ribosomal subunits of L cells

The 40S and 60S ribosomal subunits of L cells are gamma-irradiated in the absence of oxygen at low radiation doses to keep the integrity of the ribosomal structure. We show that under these experimental conditions, specific cross-links are induced in situ between rRNA and ribosomal proteins due to close contact between their reactive groups. We found that about 15 proteins are cross-linked to the 28S RNA. Most of them belong to the core proteins of the 60S ribosomal subunits. A few high-molecular mass proteins which might be factors are also bound to 28S RNA. Between 8 and 11 proteins are covalently linked to 18S RNA; 8 of these have been previously described as transferable proteins from one subunit to the other. Only 3 are core proteins of the small subunit. The contribution of these results to the study of the three-dimensional ribosomal structure is also discussed.