Members of this family of bacterial domains are predicted to be RNases (from similarities to 5'-exonucleases).
PIN domains are small protein domains identified by the presence of three strictly conserved acidic residues. Apart from these three residues, there is poor sequence conservation [PUBMED:21036780]. PIN domains are found in eukaryotes, eubacteria and archaea. In eukaryotes they are ribonucleases involved in nonsense mediated mRNA decay [PUBMED:17053788] and in processing of 18S ribosomal RNA [PUBMED:19706509]. In prokaryotes, they are the toxic components of toxin-antitoxin (TA) systems, their toxicity arising by virtue of their ribonuclease activity. The PIN domain TA systems are now called VapBC TAs(virulence associated proteins), where VapB is the inhibitor and VapC, the PIN-domain ribonuclease toxin [PUBMED:21036780].