A number of eukaryotic and archaebacterial large subunit ribosomal proteins can be grouped on the basis of sequence similarities. These proteins have 87 to 128 amino-acid residues. This family consists of:

• Yeast eL31A (also known as L34)
• Archaeal L31 [ PUBMED:2207169 ]
• Plants L31
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A number of eukaryotic and archaebacterial large subunit ribosomal proteins can be grouped on the basis of sequence similarities. These proteins have 87 to 128 amino-acid residues. This family consists of:

• Yeast eL31A (also known as L34)
• Archaeal L31 [ PUBMED:2207169 ]
• Plants L31
• Mammalian L31 [ PUBMED:3816785 ]

Ribosomal protein eL31, which is present in archaea and eukaryotes, binds the 23S rRNA and is one of six protein components encircling the polypeptide exit tunnel. It is a component of the eukaryotic 60S (large) ribosomal subunit, and the archaeal 50S (large) ribosomal subunit [ PUBMED:12554856 PUBMED:10937990 PUBMED:12007402 PUBMED:11909526 PUBMED:11904172 PUBMED:11114498 PUBMED:11297922 PUBMED:7711082 PUBMED:9657144 PUBMED:11598216 PUBMED:14976550 PUBMED:18400176 PUBMED:2597680 PUBMED:8722009 PUBMED:10937989 PUBMED:11875025 PUBMED:14561884 PUBMED:15189156 PUBMED:15334087 ].

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 ].