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The PRC-barrel: a widespread, conserved domain shared by photosynthetic reaction center subunits and proteins of RNA metabolism

Vivek Anantharaman and L Aravind*

Author Affiliations

National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA

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Genome Biology 2002, 3:research0061-research0061.9  doi:10.1186/gb-2002-3-11-research0061

Published: 14 October 2002



The H subunit of the purple bacterial photosynthetic reaction center (PRC-H) is important for the assembly of the photosynthetic reaction center and appears to regulate electron transfer during the reduction of the secondary quinone. It contains a distinct cytoplasmic β-barrel domain whose fold has no close structural relationship to any other well known β-barrel domain.


We show that the PRC-H β-barrel domain is the prototype of a novel superfamily of protein domains, the PRC-barrels, approximately 80 residues long, which is widely represented in bacteria, archaea and plants. This domain is also present at the carboxyl 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. Versions of this domain from photosynthetic proteobacteria contain a conserved acidic residue that is thought to regulate the reduction of quinones in the light-induced electron-transfer reaction. Closely related forms containing this acidic residue are also found in several non-photosynthetic bacteria, as well as in cyanobacteria, which have reaction centers with a different organization. We also show that the domain contains several determinants that could mediate specific protein-protein interactions.


The PRC-barrel is a widespread, ancient domain that appears to have been recruited to a variety of biological systems, ranging from RNA processing to photosynthesis. Identification of this versatile domain in numerous proteins could aid investigation of unexplored aspects of their biology.