<p>A group of ATP-binding proteins that includes the regulatory subunit of the ATP-dependent protease clpA; heat shock proteins clpB, 104 and 78; and chloroplastproteins CD4a (ClpC) and CD4b belong to this family [<cite idref="PUB00004102"/>, <cite idref="PUB00004707"/>]. The proteins are thought to protect cells from stress by controlling the aggregation and denaturation of vital cellular structures. They vary in size, but share a domainwhich contains an ATP-binding site.</p><p>These signatures which span the ATP binding region also identify the bacterial DNA polymerase III subunit tau (<db_xref db="EC" dbkey="2.7.7.7"/>), ATP-dependent protease La (<db_xref db="EC" dbkey="3.4.21.53"/>) and the mitochondrial lon protease homologue (<db_xref db="EC" dbkey="3.4.21"/>), both of which belong to MEROPS peptidase family S16.</p>