This superfamily entry includes the ribosomal protein S18, found in the small subunit (30S) of the bacterial ribosome, as well as eubacterial S18, metazoan mitochondrial S18, algal and plant chloroplast S18 and cyanelle S18.

S18 is thought to be involved in binding of the aminoacyl-tRNA complex, due to its location within the platform (P) region. S18 is well exposed on the surface of the E. coli ribosome, and is a secondary rRNA binding protein. Along with other ribosomal proteins (S15 and S6), S18 contributes to the formation of the tree-helix junction in the central domain of 16S rRNA (three-helix junction). The S18 protein, unlike S15 and S6, contains a single small element of regular secondary structure, yet it forms a compact structure tightly packed against S6 and the RNA.

PFAM:PF01084, INTERPRO:IPR036870,PMID:11007480,DOI:10.1126/science.288.5463.107