<p> This family consists of an exoribonuclease, ribonuclease R, also called VacB. It is one of the eight exoribonucleases reported in <taxon tax_id="562">Escherichia coli</taxon> and is broadly distributed throughout the bacteria. In E. coli, double mutants of this protein and polynucleotide phosphorylase are not viable. Not included in this entry are shorter, divergent forms from the Chlamydiae and the Campylobacterales (including <taxon tax_id="210">Helicobacter pylori</taxon>(Campylobacter pylori)) and <taxon tax_id="173">Leptospira interrogans</taxon> [<cite idref="PUB00015534"/>, <cite idref="PUB00015537"/>].</p>