Radiochemical cross-linking of proteins to RNA within ribosomal subunits from E. colil MRE 600.

Irradiation in vitro of 30S and 50S ribosomal subunits from E. coli MRE 600 by gamma rays from cobalt 60, in the absence of oxygen, results in the formation of covalent links between the RNAs and some ribosomal proteins. At low radiation doses, just sufficient to keep the integrity of the ribosome structure, the phenomenon appears highly specific. In the 30S irradiated particle, protein S1 attaches to 16S RNA; in the 50S irradiated particle, the proteins L3, L13, L19, L21, L22 and L24 are linked to 23S RNA. The mechanism of formation of these cross-links and their contribution to the study of the tridimensional ribosome structure are also discussed.