The use of sym-triazine trichloride in RNA-protein cross-linking studies with Escherichia coli ribosomal subunits.

The reagent sym-triazine trichloride is used as a bifunctional reagent to generate RNA-protein cross-links within intact ribosomal subunits from E. coli. The reaction takes place in a stepwise manner, involving substitution of one chlorine atom at 12 degrees and pH 8, and substitution of the second at 40 degrees and pH 6. The cross-linked proteins are analysed by two-dimensional electrophoresis, and the existence of a stable cross-linkage is demonstrated by isolating protein-oligonucleotide complexes from 32P-labelled subunits. The proteins cross-linked are S3 and S4 in the 30S subunit, and L2 in the large subunit, together with smaller amounts of other proteins. The reagent should prove useful in topographical studies of the E. coli ribosome as it is a rigid molecule and generates very short cross-links.