The Binding Site of Protein L1 on 23‐S Ribosomal RNA of Escherichia coli

Ribonucleoproteins were prepared by ribonuclease digestion of a reconstitued complex of ribosomal protein L 1 and 23-S RNA from Escherichia coli. Three main ribonucleoproteins were identified. The largest was only obtained in an impure state at low ribonuclease concentration, whereas the two smaller ones, which were difficult to separate from one another electrophoretically, were stable over a range of enzyme concentrations. The two smaller ribonucleoproteins yielded a total of 13 RNA subfragments that were judged to be homogeneous electrophoretically. The latter were characterized for molecular weight and the subfragment composition of each of these ribonucleoproteins was established. Furthermore, the subfragments were shown to be maintained together in each ribonucleoprotein by RNA-RNA interactions. The primary and specific binding site of protein L1 was localized on one continuous RNA subfragment of about 110 nucleotides in length by two newly developed binding methods.