The heat shock proteins HslV and HslU (HslVU complex; also known as ClpQ and ClpY respectively, or ClpQY) are expressed in many bacteria such as E. coli in response to cell stress.

[1] The hslV protein is a protease and the hslU protein is an ATPase; the two form a symmetric assembly of four stacked rings, consisting of an hslV dodecamer bound to an hslU hexamer, with a central pore in which the protease and ATPase active sites reside.

[4] HslV and hslU genes have also been identified in some eukaryotes, although these also require the constitutively expressed proteasome for survival.

[7] Translocation is also facilitated by the C-terminal tails of the HslU subunits, which form a gate closing off the proteolytic active sites in the central pore until a substrate has been bound and unfolded.

[8] The basic mechanism by which the hslVU complex undertakes proteolytic substrate degradation is essentially the same as that observed in the eukaryotic proteasome, catalyzed by Nactive-site threonine residues.