RNA-PROTEIN CROSS-LINKING IN ESCHERICHIA-COLI 50S RIBOSOMAL-SUBUNITS - DETERMINATION OF SITES ON 23S RNA THAT ARE CROSS-LINKED TO PROTEIN-L2, PROTEIN-L4, PROTEIN-L24 AND PROTEIN-L27 BY TREATMENT WITH 2-IMINOTHIOLANE

RNA-protein cross-links were introduced into Escherichia coli 50S ribosomal subunits by treatment with 2-iminothiolane followed by mild ultraviolet irradiation. After partial digestion of the RNA, the cross-linked RNA-protein complexes were separated by our recently published three-step procedure. In cases where this separation was inadequate, a further purification step was introduced, involving affinity chromatography with antibodies to the ribosomal 50S proteins. Analysis of the isolated complexes enabled four new cross-link sites on the 23S RNA to be identified, as well as re-confirming several previously established sites. The new sites are as follows: protein L2 is cross-linked within an oligonucleotide at positions 1818-1823 in the 23S RNA, protein L4 within positions 320-325, protein L24 within positions 99-107, and protein L27 within positions 2320-2323.