InterPro domain: IPR001515

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 ].

L32 is a protein from the large ribosomal subunit that contains a surface-exposed globular domain and a finger-like projection that extends into the RNA core to stabilize the tertiary structure. L32 does not appear to play a role in forming the A (aminacyl), P (peptidyl) or E (exit) sites of the ribosome, but does interact with 23S rRNA, which has a "kink-turn" secondary structure motif. L32 is overexpressed in human prostate cancer and has been identified as a stably expressed housekeeping gene in macrophages of human chronic obstructive pulmonary disease (COPD) patients. In Schizosaccharomyces pombe, L32 has also been suggested to play a role as a transcriptional regulator in the nucleus. Found in archaea and eukaryotes, this protein is known as L32 in eukaryotes and L32e in archaea [ 4 , 5 , 6 , 7 , 8 , 9 , 10 ].

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5. Stability of housekeeping genes in alveolar macrophages from COPD patients. Eur. Respir. J. 27, 300-6
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