<p> This domain is found in a large number of proteins including magnesium dependent endonucleases and phosphatases involved in intracellular signalling [<cite idref="PUB00007746"/>]. Proteins this domain is found in include: AP endonuclease proteins (<db_xref db="EC" dbkey="4.2.99.18"/>), DNase I proteins (<db_xref db="EC" dbkey="3.1.21.1"/>), Synaptojanin an inositol-1,4,5-trisphosphate phosphatase (<db_xref db="EC" dbkey="3.1.3.56"/>) and Sphingomyelinase (<db_xref db="EC" dbkey="3.1.4.12"/>).</p>