<p>Members of this protein family are about 265 residues long and each contains an S4 RNA-binding domain of about 48 residues. The member from the Cyanobacterium, <taxon tax_id="1148">Synechocystis sp.</taxon> (strain PCC 6803), was detected as a novel polypeptide in a highly purified preparation of active photosystem II [<cite idref="PUB00042838"/>]. The phylogenetic distribution, including Cyanobacteria and Arabidopsis, supports a role in photosystem II, although the high bit score cut-off for this model excludes similar sequences in non-photosynthetic organisms such as <taxon tax_id="129958">Carboxydothermus hydrogenoformans</taxon>, a Gram-positive bacterium.</p>