Photoinduced convalent crosslinkage, in situ, of Escherichia coli 50 S ribosomal proteins to rRNA.

Irradiation of aqueous solutions of Escherichia coli 50 S ribosomal subunits with 253.7 nm light results in the covalent crosslinkage of the rRNA and protein components. Neither peptide bond cleavage nor protein-protein crosslinkage accompanies the crosslinkage reactionmin addition, substantial photoinduced modifications in the primary structure of the ribosomal proteins, other than crosslinkage to rRNA, are not detected. The crosslinkage of the ribosomal proteins to the rRNA proroceeds in two discrete, dose-dependent steps. The first step, requires an input of up to 3 with 10-20 Quanta of 253.7nm radiation, and results in the crosslinkage of less than half of the ribosomal proteins to the rRNA. The second step requires an input of greater than 3 with 10-20 Quanta of 253.7 nm radiation, and results in the crosslinkage of the remaining ribosomal proteins to the rRNA. The possible relationship of the nature of the corsslinkage reaction to the spatial orientations of the rRNA and protein molecules in the intact 50 S ribosomal subunits is discussed.