DO RIBOSOMAL-RNAS ACT MERELY AS SCAFFOLD FOR RIBOSOMAL-PROTEINS

Investigations that are being carried out in various laboratories including ours clearly provide the answer which is in the negative. Only the direct evidences obtained in this laboratory will be presented and discussed. It has been unequivocally shown that the interaction between 16S and 23S RNAs plays the primary role in the association of ribosomal subunits. Further 23S RNA is responsible for the binding of 5S RNA to 16S.23S RNA complex with the help of three ribosomal proteins, L5, L18, L15/L25. The 16S.23S RNA complex is also capable of carrying out the following ribosomal functions, although to small but significant extents, with the help of a very limited number of ribosomal proteins and the factors involved in protein synthesis: (a) poly U-binding, (b) poly U-dependent binding of phenylalanyl tRNA, (c) EG-G-dependent GTPase activity, (d) initiation complex formation, (e) peptidyl transferase activity (puromycin reaction) and (f) polyphenylalanine synthesis. These results clearly indicate the direct involvement of rRNAs in the various steps of protein synthesis. Very recently it has been demonstrated that the conformational change of 23S RNA is responsible for the translocation of peptidyl tRNA from the aminoacyl (A) site to the peptidyl (P) site. A model has been proposed for translocation on the basis of direct experimental evidences. The new concept that ribosomal RNAs are the functional components in ribosomes and proteins act as control switches may eventually turn out to be noncontroversial.