<p> The fundamental activity of the ribosome is two-fold: to decode the message of the mRNA in the small subunit, and to form a peptide bond between peptidyl-tRNA and aminoacyl-tRNA by a peptidyl transferase activity in the large subunit. Several prokaryotic and eukaryotic proteins that are involved in the translation process contain an SH3-like domain. The structure of the translation protein SH3-like domain is a partly opened beta barrel, where the last strand is interrupted by a 3-10 helical turn. The structure of the RNA-binding C-terminal domain of the <taxon tax_id="1422">Bacillus stearothermophilus</taxon> (Geobacillus stearothermophilus) ribosomal protein L2 has been shown to adopt the SH3-like barrel topology [<cite idref="PUB00010714"/>]. The L2 protein is located near the peptidyl transferase centre in the large ribosomal subunit where it may contribute to peptidyl transferase activity, and is involved in the assembly of the 23SrRNA. Likewise, the N-terminal domain of the ubiquitous eukaryotic translation elongation factor 5a (IF5A) protein adopts the SH3-like barrel topology [<cite idref="PUB00010715"/>, <cite idref="PUB00010716"/>]. IF5A, previously thought to be an initiation factor, is now considered to be involved in translation elongation [<cite idref="PUB00046010"/>] and in cell-cycle regulation. IF5A acts as a cofactor of the Rev protein in HIV-1-infected cells and of the Rex protein in T-cell leukaemia virus 1-infected cells. </p>