Evidence for RNA-RNA cross-link formation in Escherichia coli ribosomes

Evidence is presented in three separate cases for the forma-tion of RNA-RNA cross-links in intact E. coli ribosomes and ribo-somal subunits. The first case is a cross-link between the 18S and 13S regions of the 23S RNA, induced by ultraviolet irradia-tion. The second is a cross-link at the subunit interface, gene-rated by the bifunctional reagent bis-(2-chloroethyl)-amine. The third example is a cross-link between sections O'-D and P-A of the 16S RNA, induced as in the first case by ultraviolet irradia-tion. The RNA-RNA cross-links can be identified as such, despite the complications introduced by concomitant RNA-protein cross-linking reactions. The experiments represent a first attempt to introduce RNA-RNA cross-linking into studies of the topographical organization of the RNA within the ribosome