The three-dimensional structure of the RNA-binding domain of ribosomal protein L2; a protein at the peptidyl transferase center of the ribosome

Ribosomal protein L2 is the largest protein component in the ribosome. It i s located at or near the peptidyl transferase center and has been a prime c andidate for the peptidyl transferase activity. It binds directly to 23S rR NA and plays a crucial role in its assembly. The three-dimensional structur e of the RNA-binding domain of L2 from Bacillus stearothermophilus has been determined at 2.3 Angstrom resolution by X-ray crystallography using the s elenomethionyl MAD method. The RNA-binding domain of L2 consists of two rec urring motifs of similar to 70 residues each. The N-terminal domain (positi ons 60-130) is homologous to the OR-fold, and the C-terminal domain (positi ons 131-201) is homologous to the SH3-like barrel. Residues Arg86 and Arg15 5, which have been identified by mutation experiments to be involved in the 23S rRNA binding, are located at the gate of the interface region between the two domains. The molecular architecture suggests how this important pro tein has evolved from the ancient nucleic acid-binding proteins to create a 23S rRNA-binding domain in the very remote past.