Crystal structure of a ribosomal component at 2.6 Å resolution

Structural information about the ribosomes has been sought in many ways 1,2 . It is known that the 50S subunit of Escherichia coli ribosomes contains four copies of the ribosomal protein L7/L12 (refs 3–7) in a unique region 8,9 . A complex can be isolated consisting of those four copies bound to another ribosomal protein, L10 (refs 10–13). L7/L12 aggregates into elongated dimers in solution 14,15 . Ribosomes deprived of L7/L12 have a reduced affinity for supernatant factors such as EF-Tu and EF-G and almost no capacity for factor-dependent GTP hydrolysis 16–18 . The sequence of the 120 amino acid residues in L7/L12 from E. coli has been determined 19 , and two domains of L7/L12 (residues 1–36 and 53–120, respectively) have been crystallized separately 20 . We now report the first crystal structure of a ribosomal component, a C-terminal fragment (CTF) of the protein L7/L12 from E. coli , determined to 2.6 Å resolution. The CTF has a compact, plum-shaped tertiary structure with a high content of secondary structure. The three α -helices and three β -strands in CTF account for 32% α -helix and 14% β -structure in the intact L7/L12 protein. A binding site for anions shows some resemblance to the known nucleotide binding site in many proteins.