This superfamily represents the Brix (biogenesis of ribosomes in Xenopus) domain, first characterised in the Brix protein. It is a structural domain found in a variety of proteins from different species, such as archaea and eukaryotes: Peter Pan (D. melanogaster) and SSF1/2 (S.cerevisiae), RPFAM:PF1 (S. cerevisiae), IMP4 (S. cerevisiae), Brix (X.laevis) and BRX1 (S. cerevisiae) and RPFAM:PF2 (S.cerevisiae).

Typically, a protein sequence belonging to the Brix domain superfamily contains a highly charged N-terminal segment (about 50 residues) followed by a single copy of the Brix domain and another highly charged C-terminal region (about 100 residues). The archaean sequences have two unique characteristics: (1) the charged regions are totally absent at the N terminus and are reduced in number to about 10 residues at the C terminus; and (2) the C-terminal part of the Brix domain itself is minimal. Two eukaryote groups have large insertions within the C-terminal region: about 70 residues in the group III and about 120 in the group II. Biological data for some proteins in this family suggest a role in ribosome biogenesis and rRNA binding.

PFAM:PF04427, INTERPRO:IPR007109,PMID:11406393,PMID:11246005