<p>ClpX is a member of the HSP (heat-shock protein) 100 family. Gel filtration and electron microscopy showed that ClpX subunits associate to form a six-membered ring that is stabilised by binding of ATP or nonhydrolysable analogs of ATP [<cite idref="PUB00015582"/>]. It functions as an ATP-depedent [<cite idref="PUB00015582"/>] molecular chaperone and is the regulatory subunit of the ClpXP protease [<cite idref="PUB00011891"/>].</p><p>ClpXP is involved in DNA damage repair, stationary-phase gene expression, and ssrA-mediated protein quality control. To date more than 50 proteins include transcription factors, metabolic enzymes, and proteins involved in the starvation and oxidative stress responses have been identified as substrates [<cite idref="PUB00011892"/>]. </p><p>The N-terminal domain of ClpX is a C4-type zinc binding domain (ZBD) involved in substrate recognition. ZBD forms a very stable dimer that is essential for promoting the degradation of some typical ClpXP substrates such as lO and MuA [<cite idref="PUB00011897"/>]. </p>