<p>This family is defined to identify a pair of paralogous 3'->5' exoribonucleases in <taxon tax_id="562">Escherichia coli</taxon>, plus the set of proteins apparently orthologous to one or the other in other eubacteria. VacB was characterised originally as required for the expression of virulence genes, but is now recognised as the exoribonuclease RNase R (Rnr). Its paralog in <taxon tax_id="562">Escherichia coli</taxon> and <taxon tax_id="727">Haemophilus influenzae</taxon> is designated exoribonuclease II (Rnb) [<cite idref="PUB00015537"/>]. Both are involved in the degradation of mRNA, and consequently have strong pleiotropic effects that may be difficult to disentangle. Both these proteins share domain-level similarity (RNB, S1) with a considerable number of other proteins, and full-length similarity scoring below the trusted cut-off to proteins associated with various phenotypes but uncertain biochemistry; it may be that these latter proteins are also 3' exoribonucleases.</p>