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 γ‐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.