Ribosomal protein L7A/L8 (IPR001921)

Short name: Ribosomal_L7A/L8

Overlapping homologous superfamilies


Family relationships


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 [PMID: 11297922, PMID: 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 [PMID: 11290319, PMID: 11114498].

The genomic structure and sequence of the human ribosomal protein L7a has been determined [PMID: 1756182]. The gene contains 8 exons and 7 introns, encompassing 3179 bp. The human gene resembles other mammalian ribosomal protein genes in so far as it contains a short first exon, a short 5' untranslated leader and its transcriptional start sites at C residues embedded in a poly-pyrimidine tract [PMID: 1756182].

The sequence of a gene for ribosomal protein L4 of Saccharomyces cerevisiae (Baker's yeast) has also been determined, which, unlike most of its other ribosomal protein genes, has no intron [PMID: 2183194]. The single open reading frame is highly similar to mammalian ribosomal protein L7a.

There appear to be two genes for L4, both of which are active [PMID: 2183194]. Yeast cells containing a disruption of the L4-1 gene form smaller colonies than either wild-type or disrupted L4-2 strains. Disruption of both L4 genes is lethal, probably resulting from an inability of the organism to produce functional ribosomes [PMID: 2046660].

Several other ribosomal proteins have been found to share sequence similarity with L7a, including yeast NHP2 [PMID: 2063628], Bacillus subtilis hypothetical protein ylxQ, Haloarcula marismortui (Halobacterium marismortui) Hs6, and Methanocaldococcus jannaschii MJ1203.

This InterPro entry focus on regions that characterise the ribosomal L7A proteins but distinguish them from the rest of the HMG-like family.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.