<p>These proteins represent ribonuclease D, a 3-exonuclease shown to act on tRNA both in vitro and when overexpressed in vivo. Members of this family are restricted to the Proteobacteria; Aquifex, Mycobacteria and eukaryotes. Ribonuclease D is not essential in <taxon tax_id="562">Escherichia coli</taxon> but is deleterious when overexpressed. The precise biological role of ribonuclease D is still unknown. </p>