A hyperconserved protein in Prochlorococcus and marine Synechococcus.

An ORF (encoding a hyperconserved protein of unknown function) in Prochlorococcus/marine Synechococcus genomes that is 100% conserved on the amino acid level but lacks homologs outside this group is described here. Such conservation of an uncharacterized group-specific gene is unusual, and unexpected given the extensive genomic divergence of this group at other loci. Comparative analyses indicate that the hyperconserved protein, which may be involved in interactions with nucleic acids, is under stabilizing selection and has resided in these genomes since the last common ancestor of the group.