<p>The PRC-barrel is an all beta barrel domain found in photosynthetic reaction centre subunit H of the purple bacteria. PRC-barrels are approximately 80 residues long, and found widely represented in bacteria, archaea and plants. This domain is also present at the C terminus of the pan-bacterial protein RimM, which is involved in ribosomal maturation and processing of 16S rRNA. A family of small proteins conserved in all known euryarchaea are composed entirely of a single stand-alone copy of the domain [<cite idref="PUB00010437"/>].</p>