Photo-induced protein-RNA cross-linking in mammalian 40-S ribosomal subunits

RNA-protein interaction in the 40-S subunits of rat liver ribosomes were studied by measuring cross-linking of proteins to RNA induced by ultraviolet radiation. Under conditions which caused neither extensive degradation of the 40-S subunits (or 18-S RNA) nor biological inactivation, the total staining intensity of the proteins extracted from irradiated subunits was considerably reduced on the two-dimensional electrophoregrams. Convincing evidence was obtained that cross-linking of the proteins to 18-S RNA was the predominant reaction. The cross-linking extent of the individual proteins was studied as a function of the radiation dose. At 4 degree C, 13--15 proteins were found to cross-linked to RNA even at low doses of quanta. They generally correspond to proteins which have been previously shown to react poorly on the ribosomes with various chemical reagents. At 25 degree C, all the proteins became cross-linked to RNA using the same radiation doses.