This entry represents the L40 ribosomal domain from both archaea and eukaryotes.

In eukaryotes, L40 is fused to ubiquitin moieties, and this fusion protein is known as Ubiquitin-ribosomal protein eL40 fusion protein or UBL40 [ PUBMED:7488009 PUBMED:16185873 … expand

This entry represents the L40 ribosomal domain from both archaea and eukaryotes.

In eukaryotes, L40 is fused to ubiquitin moieties, and this fusion protein is known as Ubiquitin-ribosomal protein eL40 fusion protein or UBL40 [ PUBMED:7488009 PUBMED:16185873 ]. Specific endopeptidases cleave these precursor molecules to release ubiquitin moieties [ PUBMED:15571815 ]. UBL40 plays important roles in gametogenesis [ PUBMED:22297692 PUBMED:25208476 ]. This fusion may also have a pre-cleavage function in ribosome assembly [ PUBMED:16185873 ]. In Saccharomyces cerevisiae, eL40 is essential for translation of a subset of cellular transcripts, including stress response transcripts, such as DDR2 [ PUBMED:23169626 ]. In humans, it has been reported to be required for cap-dependent translation of vesicular stomatitis virus mRNAs [ PUBMED:32669547 ].

In archaea and some eukaryotic species such as Candida albicans, this domain covers the whole length of the protein, which is known as Large ribosomal subunit protein eL40 [ PUBMED:35613268 ].

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 [ PUBMED:11297922 PUBMED:11290319 ]. 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 [ PUBMED:11290319 PUBMED:11114498 ].