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 (By similarity). The HslVU protease complex functions in mitochondrial DNA replication by regulating DNA helicase PIF2 protein levels. 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 (HslVU) is dependent on binding of ATP (By similarity). Associated with kinetoplast DNA (kDNA). Belongs to the ClpX chaperone family. HslU subfamily.