ATPase subunit of a proteasome-like degradation complex; this subunit has chaperone activity. The binding of ATP and its subsequent hydrolysis by HslU are essential for unfolding of protein substrates subsequently hydrolyzed by HslV. HslU recognizes the N-terminal part of its protein substrates and unfolds these before they are guided to HslV for hydrolysis. A double ring-shaped homohexamer of HslV is capped on each side by a ring-shaped HslU homohexamer. The assembly of the HslU/HslV complex is dependent on binding of ATP. Belongs to the ClpX chaperone family. HslU subfamily.