Adapter protein required for efficient degradation of Spx by ClpXP under non-stress conditions (PubMed:17908206, PubMed:19074380, PubMed:24942655). Interaction with Spx stabilizes Spx and exposes the C-terminus of Spx for recognition and proteolysis by ClpXP (PubMed:24942655, PubMed:27191337). Is specific for Spx and does not enhance proteolysis by ClpCP protease (PubMed:19074380). Probably binds 2 zinc ions (PubMed:19074380). Irreversible aggregation upon several stress conditions prevents interaction with Spx and therefore leads to Spx stabilization (PubMed:25353645). Inhibited by interaction with SpxO/YuzO (PubMed:21378193). Interacts with Spx (PubMed:19074380, PubMed:24942655, PubMed:27191337). Interacts with SpxO/YuzO (PubMed:21378193). Soluble under non-stress conditions and aggregates in response to stress conditions such as disulfide stress, heat and ethanol. Expressed throughout cell growth. Negatively influences its own expression. The histidine-rich N terminus is essential for interaction with Spx. Strains lacking this gene show poor growth, affected sporulation, complete loss of competence development and overproduce Spx under unperturbed growth. Mutants also overproduce TrxA and show reduced sensitivity to disulfide stress. Belongs to the SpxH family.