Ribosomal protein L2 is involved in the association of the ribosomal subunits, tRNA binding to A and P sites and peptidyl transfer

Ribosomal proteins L2, L3 and L4, together with the 23S RNA, are the main c andidates for catalyzing peptide bond formation on the 50S subunit, That L2 is evolutionarily highly conserved led us to perform a thorough functional analysis with reconstituted 50S particles either lacking L2 or harboring a mutated L2. L2 does not play a dominant role in the assembly of the 50S su bunit or in the fixation of the 3'-ends of the tRNAs at the peptidyl-transf erase center. However, it is absolutely required for the association of 30S and 50S subunits and is strongly involved in tRNA binding to both A and P sites, possibly at the elbow region of the tRNAs, Furthermore, while the co nserved histidyl residue 229 is extremely important for peptidyl-transferas e activity, it is apparently not involved in other measured functions. None of the other mutagenized amino acids (H14, D83, S177, D228, H231) showed t his strong and exclusive participation in peptide bond formation. These res ults are used to examine critically the proposed direct involvement of His2 29 in catalysis of peptide synthesis.