InterPro domain: IPR043141

Ribosomes are the particles that catalyse mRNA-directed protein synthesis in all organisms. The codons of the mRNA are exposed on the ribosome to allow tRNA binding. This leads to the incorporation of amino acids into the growing polypeptide chain in accordance with the genetic information. Incoming amino acid monomers enter the ribosomal A site in the form of aminoacyl-tRNAs complexed with elongation factor Tu (EF-Tu) and GTP. The growing polypeptide chain, situated in the P site as peptidyl-tRNA, is then transferred to aminoacyl-tRNA and the new peptidyl-tRNA, extended by one residue, is translocated to the P site with the aid the elongation factor G (EF-G) and GTP as the deacylated tRNA is released from the ribosome through one or more exit sites [ 1 , 2 ]. About 2/3 of the mass of the ribosome consists of RNA and 1/3 of protein. The proteins are named in accordance with the subunit of the ribosome which they belong to - the small (S1 to S31) and the large (L1 to L44). Usually they decorate the rRNA cores of the subunits.

Many ribosomal proteins, particularly those of the large subunit, are composed of a globular, surfaced-exposed domain with long finger-like projections that extend into the rRNA core to stabilise its structure. Most of the proteins interact with multiple RNA elements, often from different domains. In the large subunit, about 1/3 of the 23S rRNA nucleotides are at least in van der Waal's contact with protein, and L22 interacts with all six domains of the 23S rRNA. Proteins S4 and S7, which initiate assembly of the 16S rRNA, are located at junctions of five and four RNA helices, respectively. In this way proteins serve to organise and stabilise the rRNA tertiary structure. While the crucial activities of decoding and peptide transfer are RNA based, proteins play an active role in functions that may have evolved to streamline the process of protein synthesis. In addition to their function in the ribosome, many ribosomal proteins have some function 'outside' the ribosome [ 3 , 3 ].

This superfamily represents the N-terminal RNA-binding domain of the ribosomal protein L10 found in the large subunit (50S) of the bacterial ribosome. The entry contains homologues such as archaebacterial acidic ribosomal protein P0 homologue (L10E) and the eukaryotic 60S ribosomal protein P0 (L10E). The RNA-binding domain and the adjacent domain are thought to exist in archaeal L10 and eukaryotic P0 proteins only. Structurally, this domain contains three alpha-helices on each side of the five-stranded anti-parallel beta-sheet.

The large ribosomal subunit contains a highly flexible and functionally important lateral protuberance called the 'stalk' (L7/L12 stalk in Bacteria, L12 stalk in Archaea, and P1/P2 stalk in Eukarya). The stalk is involved in the formation of the so-called 'GTPase-associated site' and plays a key role in the interaction of ribosome with translation factors and in the control of translation accuracy [ 4 ]. The L7/12 stalk is formed by two or three copies of the L7/L12 dimer bound to the C-terminal tail of protein L10 [ 5 ]. The N-terminal domain of L10 binds to a segment of domain II of 23S rRNA near the binding site for ribosomal protein L11 [ 6 ].

1. Atomic structures at last: the ribosome in 2000. Curr. Opin. Struct. Biol. 11, 144-54
2. The ribosome in focus. Cell 104, 813-6
3. The end of the beginning: structural studies of ribosomal proteins. Curr. Opin. Struct. Biol. 10, 633-6
4. Structure of a two-domain N-terminal fragment of ribosomal protein L10 from Methanococcus jannaschii reveals a specific piece of the archaeal ribosomal stalk. J. Mol. Biol. 399, 214-20
5. Structural basis for the function of the ribosomal L7/12 stalk in factor binding and GTPase activation. Cell 121, 991-1004